Clock control circuits, systems and methods

Abstract: A microprocessor device (102) includes a central processing unit (702) having a clock input, a clock generator (OSC, PLL) of clock pulses, a logic circuit (708) having an output to supply a clock control signal (SUPS), and a clock gate (3610) fed by the clock pulses and having a clock gate output (CPU_CLK) coupled to the clock input of the central processing unit. The clock gate (3610) responds to the clock control signal (SUPS) to prevent said clock pulses (CPU_CLK) from reaching the central processing unit within one clock cycle of a change in said clock control signal. Other devices, systems and methods are also disclosed.

Description: FIELD OF THE INVENTION This invention generally relates to electronic circuits, computer systems and methods of operating them. BACKGROUND OF THE INVENTION Without limiting the scope of the invention, its background is described in connection with computer systems, as an example. Early computers required large amounts of space, occupying whole rooms. Since then minicomputers and desktop computers entered the marketplace. Popular desktop computers have included the "Apple" (Motorola 680x0 microprocessor-based) and "IBM-compatible" (Intel or other x86 microprocessor-based) varieties, also known as personal computers (PCs) which have become very popular for office and home use. Also, high-end desk top computers called workstations based on a number of superscalar and other very-high-performance microprocessors such as the SuperSPARC microprocessor have been introduced. In a further development, a notebook-size or palm-top computer is optionally battery powered for portable user applications. Such notebook and smaller computers challenge the art in demands for conflicting goals of miniaturization, ever higher speed, performance and flexibility, and long life between battery recharges. Also, a desktop enclosure called a docking station has the portable computer fit into the docking station, and improvements in such portable-computer/docking-station systems are desirable. Improvements in circuits, integrated circuit devices, computer systems of all types, and methods to address all the just-mentioned challenges, among others, are desirable, as described herein. Document WO-A-93/06543 discloses a portable computer with a power-saving "sleep" mode. SUMMARY OF THE INVENTION According to the present invention there are provided a clock control circuit and a method of operating a computing system as defined in the appended claims. BRIEF DESCRIPTION OF THE DRAWINGS In the drawings: FIG. 1 is a pictorial diagram of two notebook computer embodiments, one of them being inserted into a docking station embodiment to provide a combined system embodiment; FIG. 2 is a right-side profile view, plan view, and rear elevation of the combined system of notebook and docking station of FIG. 1; FIG. 3 is an electrical block diagram of the FIG. 1 combined embodiment system of improved notebook computer and docking station system to which the notebook computer system connects; FIG. 4 is an electrical block diagram of another embodiment of an improved computer system for desktop, notebook computer and docking station applications; FIGS. 5, 6 and 7 are three parts of a more detailed electrical diagram (partially schematic, partially block) of a preferred embodiment electronic computer system for use in embodiments including those of FIGS. 3 and 4, wherein FIG. 5 shows MPU and PCU, FIG. 6 shows PPU and peripherals, and FIG. 7 shows display and other elements; FIG. 8 is a plan view of a preferred embodiment apparatus having a printed wiring board and electronic components of the computer system of FIGS. 5-7; FIG. 9 is a block diagram of a microprocessor unit (MPU) device embodiment for the system of FIGS. 5-7; FIG. 10 is a plan view of an integrated circuit with improved topography for implementing the microprocessor unit of FIG. 9; FIG. 11 is a block diagram of a peripheral processing unit (PPU) device embodiment for implementing the PPU in the system of FIGS. 5-7; FIG. 12 is a plan view of an integrated circuit with improved topography for implementing the peripheral processng unit of FIG. 11; FIG. 13 is an electrical block diagram of another embodiment of an improved computer system for desktop and other applications; FIG. 14 is a more detailed block diagram of a bus interface block for the embodiment of FIG. 11; FIG. 15 is a more detailed block diagram of DMA (Direct Memory Access) circuity relating to the circuitry embodiments of FIGS. 11 and 14; FIG. 16 is a block diagram of an improved BIOS addressing circuit interconnecting the PPU of FIG. 11 with a BIOS flash memory; FIG. 17 is a block diagram of interconnection of the PPU of FIG. 11 with BIOS ROM, KBC (Keyboard Controller), add-on chips and IDE hard disk drive in the system embodiment of FIGS. 5-7; FIG. 18 is a block diagram of a peripheral control unit (PCU) device embodiment to accept insertable cards for the system of FIGS. 5-7; FIG. 19 is a plan view of an integrated circuit with improved topography for implementing the peripheral control unit of FIG. 18; FIG. 20 is a block diagram of selected power and control interconnections between the MPU, PCU, PPU, power supply, display circuitry and peripherals in the system embodiment of FIGS. 5-7; FIG. 21 is a partially block, partially schematic diagram of a PPU circuit embodiment connecting to ON/OFF and SUSPEND/RESUME button circuitry, docking station connector circuitry and a power supply in various circuit embodiments; FIG. 22 is a block diagram of a part 920B of a power management circuit embodiment for use in a PPU of FIG. 11; FIG. 23 is a state transition diagram of power management states in a preferred embodiment of the power management system of FIG. 22, as well as circuitry for same and method of operation; FIG. 24 is a block diagram of another part 920A of the power management circuit embodiment in the PPU of FIG. 11; FIG. 25 is a partially schematic and partially block diagram of a timers block 2350 in FIG. 24; FIG. 26 is a partially schematic and partially block diagram of a non-linear timer embodiment for use in some of the timers of FIG. 25; FIG. 27 is a partially schematic and partially block diagram of a mask clock generator 2340 embodiment in FIG. 23 connected to clock circuitry in the MPU of FIGS. 5, 9, 33 and 36, together with waveform diagrams; FIG. 28 is a partially schematic and partially block diagram of a system management interrupt circuitry 2370 embodiment in FIG. 24; FIG. 29 is a waveform diagram of clock signals and control signals showing an improved method of operation and further describing the operation of the SMI circuitry of FIG. 28; FIG. 30 is a further waveform diagram of clock signals and control signals showing an improved method of operation and further describing the operation of the SMI circuitry of FIG. 28; FIG. 31 is a partially schematic and partially block diagram of a system management interrupt circuitry 1620 embodiment in the PCU of FIG. 18 which is interconnected with the PPU of FIG. 11 and MPU of FIG. 9 to form a distributed power management system embodiment of FIGS. 31, 28, 33 and 34 interrelated with the computer system embodiment of FIGS. 5-7; FIG. 32 is a waveform and process of operation diagram of clock signals and control signals in circuitry of FIG. 34 in the MPU of FIG. 5; FIG. 33 is a schematic diagram of a power management circuitry embodiment in the MPU supplied with the signals of FIGS. 32 and 34; FIG. 34 is a further schematic diagram of a power management circuitry embodiment in the MPU for supplying a Resume signal to the circuitry of FIG. 33; FIG. 35 is a waveform and process of operation diagram for selected signals in the circuitry of FIG. 33; FIG. 36 is a partially block, partially schematic diagram of a clocking and control circuitry embodiment of the MPU of FIG. 5; FIG. 37 is a block diagram of frequency-determining crystal connections and clock lines in the system embodiment of FIG. 5-7; FIG. 38 is a block diagram showing an interrupt routing system using one or more PCUs connected to an interrupt routing circuitry embodiment in the PPU, with outputs for connection to the MPU, detailing the system embodiment of FIGS. 5-7; FIG. 39 is a waveform and process of operation diagram for selected signals in the circuitry of FIG. 38; FIG. 40 is a process of operation diagram for fair rotation in arbitration; FIG. 41 is a more detailed process of operation diagram for arbitration by the arbiter 906 of the PPU of FIG. 11; FIG. 42 is a more detailed block diagram of a fast internal PPU bus 904 with parallel port 938 embodiment of the PPU of FIG. 11; FIG. 43 is a more detailed block diagram of interrupt routing circuitry in the PPU of FIG. 38; FIG. 44 is a more detailed block diagram each interrupt controller block of FIG. 43; FIG. 45 is a flow diagram of a process or method of operation of the preferred embodiment system of FIGS. 5-7; FIG. 46 is a flow diagram of a process or method of operation for power management adjustment of a TONTOFF register of FIG. 27 in the preferred embodiment system of FIGS. 5-7; FIG. 47 is a block diagram of a system activity timer embodiment alternative to the embodiment of FIG. 25; FIG. 48 is a block diagram of a keyboard polling monitor circuit embodiment for use in the SMI circuit embodiment of FIG. 28; FIG. 49 is a block diagram of an adaptive CPU clock control system and method for power management; FIG. 50 is a schematic diagram of a system environment sensing circuit; FIG. 51 is a block diagram of power supply connections for a system of FIGS. 5-7; FIG. 52 is a partially block, partially schematic diagram of a power supply circuit in the system of FIGS. 6, 8, 20 and 21; FIG. 53 is a block diagram of a temperature sensing and control circuit embodiment for implementation in FPGA 124 of FIG. 6; FIG. 54 is a block diagram of another temperature sensing and control circuit embodiment for implementation in FPGA 124 of FIG. 6; FIG. 55 is a schematic diagram of a circuitry embodiment for reducing power dissipation at a boundary between differing-voltage areas of the PPU also shown in FIGS. 6, 11, 12, and 20-22; Corresponding numerals and symbols in the different figures refer to corresponding parts unless otherwise indicated. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS In FIG. 1 a notebook-computer-and-docking-station system 5 has an insertable or dockable notebook computer 6 shown being inserted along a path of bold arrows into a docking station 7. A CRT (cathode ray tube) display 8, a keyboard 9 and a mouse 10 are respectively connected to mating connectors on a rear panel of docking station 7. Docking station 7 has illustratively four storage access drives, for example: 5.25 inch floppy disk drive 11, 3.5 inch floppy disk drive 12, a CD (compact disk) drive 13 and an additional floppy or CD drive 14. Docking station 7 has a docking compartment 15 into which notebook computer 6 inserts securely against internal rear electrical connectors. Docking compartment 15 in this embodiment accepts manual insertion of notebook computer 6 along lateral guideways 16 and 17 using a minimum of mechanical elements to achieve advantageous economy in cost of the physical docking . A horizontal surface of guideway brackets or a horizontal panel as shown provide physical support for notebook computer 6. In an alternative embodiment, a motorized insertion mechanism associated with docking compartment 15 holds, rearwardly moves and seats notebook computer 6 against either rear electrical connectors, lateral connectors or both. Docking station 7 in this embodiment occupies a volume V = LWH equal to the product of the length L, width W and height H of the form of a rectangular solid. Notebook computer 6 also has a form of a rectangular solid with volume v = l w h equal to the product of its own length l, width w, and height h. The docking station 7 in this embodiment advantageously is proportioned so that the width w of the notebook 6 exceeds at least 75% and preferably 85% of the width W of the docking station. In this way, the room left for keyboard 9 and user work space to the front of keyboard 9 is advantageously sufficient to make docking station 7 as convenient to locate as many conventional desktop computers. Drives are stacked in pairs 11, 12 and 13, 14 providing extra ergonomically desirable height (user head position level, low glare) for supporting display 8, reduced length L, and efficient use of volume V. The weight distribution of the docking station 7 suits it for location on a desktop as shown, or for tower positioning with docking station 7 resting on its right side-panel. In either position, the drives 11,12 and 13,14 are suitable as shown, or alternatively are mounted with the docking compartment 15 located centrally between drives 11 and 13 on top, and drives 12 and 14 on the bottom. Notebook computer 6 has slits 18 for advantageous lateral ventilation both in open air, and in a forced air ventilation environment of docking station 7. Notebook computer 6 features front-facing slots of a 3.5 inch floppy disk drive 19 and a card connector 20 (e.g. for flash memory, modem or other insertable cards). These slots are accessible even when the notebook computer 6 is docked. An display panel 21 combined with a high-impact back panel is hingeably mounted rearward on a nigh-impact mounting base 22, Looking co the left in FIG. 1 is an identical but distinct notebook computer unit 6'. (For economy of notation, additional numerals on notebook unit 6' are not primed.) Notebook unit 6' has display panel 21 raised to operating position relative to base 22 in the portable environment. A 3.5 inch floppy diskette 23 and a flash memory card 24 are shown near their respective insertion slits 19 and 20. A keyboard 25 mounts forwardly on base 22. To the rear of keyboard 25, and between keyboard 25 and display panel 21, lie (in order from right to left) a recessed trackball 26 in a recess 27, an ON/OFF switch 28, ventilation slits 29, a a loudspeaker 30 beneath a protective grille, further ventilation slits 31, and a SUSPEND/RESUME switch 32. A physical protuberance or stud 33 is molded integral with display panel 21 or affixed thereon, near a hinge so that when the display panel 21 is closed against base 22, the stud 33 impinges against SUSPEND/RESUME switch 32 thereby putting the computer 6' in a Suspend mode whereby very little power is consumed. Then when the panel 21 is reopened, the computer resumes almost immediately with the current application program without rebooting. ON/OFF switch 28 has no stud associated with it, so that the user has the manual option to turn the notebook computer on or off and to reboot when desired. In still further features, notebook computers 6 and 6' have a display brightness (e.g. backlighting) adjustment control 34 mounted low on the right side of panel 21. An optional power supply 35 is powered from a commercial power source to which an AC plug 36 connects. Power supply 35 in turn supplies battery recharge and supply voltages via a rear power connector 37 to notebook computer 6'. An infrared (IR) emitter/detector assembly 38 on notebook computer 6 provides two-way communication with a corresponding infrared emitter/detector assembly on the back of notebook computer 6'. The two computers 6 and 6' suitably communicate directly to one another when two users are positioned opposite one another or otherwise such that the computers 6 and 6' have the IR assemblies in line-of-sight. When the two computers 6 and 6' are side-by-side, they still advantageously communicate by reflection from an IR-reflective surface 39, such as the wall of a conference room or side-panel of an overhead projector unit. Docking station 7 has an AC power plug 40 connected to energize the docking station circuitry as well as that of notebook computer 6 when the latter is inserted into docking compartment 15. An AC Power On/Off switch 41 is manually actuated by the user on the upper right front panel of docking station 7 in FIG. 1. Turning now to FIG. 2, notebook computer 6 is shown inserted against a power connector 45 of docking station 7 in a right profile view of the assembly. A hard disk drive HDD and a power supply P.S. are visible in the right profile view and in the plan view of FIG. 2. A ventilation fan 46 efficiently, quietly and with low electromagnetic interference, draws a lateral air flow across a Docking PCB (Printed Circuit Board) of the docking station, as well as through the notebook computer 6 having its own printed circuit board. The ventilation flow continues through the ventilation holes of power supply P.S. whereupon heated air is exhausted by fan 46 broadside and outward from the rear panel of docking station 7, as shown in the rear elevation detail of FIG. 2. The Docking PCB is supported low to the bottom panel 47 of an enclosure or cabinet of the docking station 7. As seen from the rear in FIG. 2, the enclosure has a left bay 48 for hard disk drive HDD and power supply P.S., a wider middle bay 49 having mass storage drives 11, 12, 13 and 14, and the docking PCB beneath the docking compartment 15, and then a right bay 50 into which a multimedia board 51, a video teleconferencing board 52, and other boards of substantial size readily fit from top to bottom of the enclosure. For convenience and economy, several connectors 55 are physically mounted and electrically connected to Docking PCB and are physically accessible through a wide aperture in the rear of the enclosure. As shown in rear elevation in FIG. 2, connectors 55 include a keyboard connector KBD, a mouse connector MS, a display connector VGA, a PRINTER port, a GAME port, a local area network LAN connector, and an RJ-11 telephone jack or modem port. A Multimedia connector and a teleconferencing Camera connector are accessible at the rear of the right bay 50. Emphasizing now the connector arrangement of the notebook computer 6 in rear elevation, a series of these connectors are physically mounted and electrically connected to an internal printed circuit board of notebook computer 6. These connectors are utilized in two docking station and system embodiments. In a first embodiment, shown in FIG. 2, an aperture-defining rectangular edge 58 provides physical access to several of the connectors of notebook computer 6, thereby increasing the connectivity of the combined system 6,7 to peripheral units as discussed in connection with FIG. 3. In a second embodiment, the edge 58 is absent, and rear connectors of the docking station 7 mate to these several connectors of notebook computer 6 as discussed in connection with FIG. 4. Looking from left to right in rear elevation of FIG. 2, a power and telephone connector 45 securely mounted to docking station 7 mates to notebook computer 6. A telephone connector 59 of notebook 6 is suitably obscured in the docking compartment 15, but available for use when the notebook is used in the portable environment. Next a display connector 60, a printer parallel port connector 61, and a disk drive connector 62 are provided at the back of notebook 6. An optional mouse connector 63 and keyboard connector 64 are provided next to IR emitter/detector 38. At far right rear on notebook 6, a high-speed bus connector 65 mates securely to a corresponding connector of docking station 7 so that wide-bandwidth communication, such as by a PCI (Peripheral Component Interconnect) type of bus is established between notebook 6 and docking station 7. In this way, the notebook 6 contributes importantly to the computing power of the combined system 5 comprised of notebook 6 and docking station 7. The physical presence of connector 45 on the left rear and connector 65 on the right rear also contribute to the security of alignment and seating of the notebook 6 in the docking compartment 15. Wide snap-springs of docking compartment 15 click into shallow mating recesses of notebook 6, completing the physical security of alignment and seating of notebook 6 in docking compartment 15. In FIG. 3, the docking station PCB has a docking station power supply 69 supplying supply voltage VCC to the components of the docking station. Power supply 69 has Power On/Off switch 41, power plug 40, and supplies operating and battery recharging power along power lines 70 through connector 45 to notebook computer 6 which has a printed circuit board and system 100 of interconnected integrated circuits therein as described more fully in connection with FIGS. 5-7 and the later Figures of drawing. In the docking station PCB, a main bus 71, such as a high bandwidth PCI bus, interconnects via buffers 72, connector 65 and buffers 73 with a high bandwidth bus 104 in system 100 of notebook 6. A docking station microprocessor unit MPU and memory circuitry 74 preferably provides advanced superscalar computing power connected to bus 71. A display interface 76 receives display data and commands from bus 71 and supplies video data out to CRT display monitor 8. A SCSI interface 77 communicates with bus 71 and can receive and send data for any suitable SCSI peripheral. Video input circuit 52 receives video data from a video camera, video recorder, or camera-recorder (CAMERA) and supplies this data to bus 71 for processing. A LAN (Local Area Network) circuit 79 provides two-way communication between the docking station 7 and to n other computers having LAN circuits 79,1,...79.n. Token ring, Ethernet, and other advanced LANs are accommodated. An adapter 80 having an interface chip therein provides communication with any LAN system and plugs into a single same socket regardless of the LAN protocol. Such LAN circuitry is described in coassigned U.S. Patent 5,299,193 "Signal Interface for Coupling a Network Front End Circuit to a Network Adapter Circuit" issued March 29, 1994 (TI-15009). A digital signal processor circuit 81 is connected to bus 71, and is adapted for voice recognition, voice synthesis, image processing, image recognition, and telephone communications for teleconferencing and videoteleconferencing. This circuit 81 suitably uses the Texas Instruments TMS320C25, TMS320C5x, TMS320C3x and TMS320C4x, and/or TMS320C80 (MVP), DSP chips, as described in coassigned U.S. Patents 5,072,418, and 5,099,417, and as to the MVP: coassigned U.S. Patent 5,212,777 "SIMD/MIMD Reconfigurable Multi-Processor and Method of Operation" and coassigned U.S. Patent , Serial No. 08/160,116 filed November 30, 1993 "Method, Apparatus and System Method for Correlation". An interface chip 82, such as a PCI to ISA or EISA interface, connects bus 71 with a different bus 83 to which a multimedia (MIDI) card 51 is connected. Card 51 has an input for at least one microphone, musical instrument or other sound source 84. Card 51 has an output accommodating monaural, stereo, or other sound transducers 85. A SCSI card 86 interfaces a document scanner to bus 83. Still further peripherals compatible with the speed selected for bus 83 are connected thereto via an I/O interface 87 which communicates with connectors for the hard disk drive HDD, the floppy disk drive FDD 11 and 12, mouse MS 10, keyboard KBD 9, the CD-ROM drive 13 and a printer such as a laser printer. A cursory view of the notebook 6 in FIG. 3 shows that various rear connectors 60-64 are physically accessible through aperture 58 of FIG. 2 allowing still additional peripherals to be optionally connected. For example, the display connector 60 is connected to a second monitor 194 so that multiple screen viewing is available to the docking station user. Connector 59 of notebook 6 is connected through connector 45 to the RJ-11 telephone connector on the back of docking station 7 so that the user does not need to do any more than insert notebook 6 into docking station 7 (without connecting to the rear of notebook 6) to immediately obtain functionality from the circuits of notebook 6. In FIG. 4, an alternative embodiment of docking station PCB has a comprehensive connector 89 to which the connectors 60-64 of notebook 6 connect. The connectors 60-64 are not independently accessible physically through any aperture 58 of FIG. 2, by contrast with the system of FIG. 3. In this way, when notebook 6 is inserted into docking compartment 15, straight-through lines from connectors 60-64 through connector 89 pass respectively to display 8, to a PRINTER peripheral, to floppy disk drive FDD, to mouse MS, and to keyboard KBD. Comprehensive connector 89 not only accommodates lines from a bus to bus interface 90 to bus buffers 72, cascaded between buses 104 and 71, but also has an HDD path from notebook 6 to the internal hard disk drive HDD of docking station 7. The docking station of FIG. 4 has the printer, FDD, MS, KBD and HDD disconnected when the notebook 6 is removed, by contrast with the docking station and notebook system of FIG. 3. However, the docking station of FIG. 4 confers a substantial economic cost advantage, especially in situations where the user does not need to use these peripherals when the notebook 6 is removed. The docking station of FIG. 3 confers substantial flexibility and functionality advantages, especially in situations in which the docking station continues to be used by a second user when the notebook user has taken the notebook elsewhere. Docking station 7 is augmented by the data and processing power available from notebook 6, when the notebook is reinserted into docking station. Similar circuit arrangements are marked with corresponding numerals in FIGS. 3 and 4, as to docking station power supply 69, Power On/Off switch 41, power plug 40, notebook system 100, main bus 71, SCSI interface 77, video input circuit 52, LAN circuit 79, interface chip 82, multimedia card 51 and SCSI card 86. Note in FIG. 4 that the SCSI card 77 is connected to the document SCANNER peripheral, providing advantageously high bandwidth input from the scanner to the hard disk drive HDD, floppy disk drive FDD, and microprocessor unit MPU 102. CD-ROM is connected by path 95 in FIG. 4 to the ISA or EISA bus 83 in FIG. 4. Card 97 connected to bus 83 can accommodate further peripherals or, indeed, a microprocessor board so that the docking station of FIG. 4 is independently usable by second user with the notebook 6 removed. In either FIG. 3 or 4, the docking station provides A) advantageous system expandability through i) ISA/EISA slots, ii) additional HDD space, CDROM, multimedia with monaural, stereo, quadraphonic and other sound systems, and iii) wide bandwidth PCI bus 71 local bus slots. A further area of advantage B) is quick, easy connections to desired non-portable equipment through i)easier to use, bigger keyboard, ii) bigger, higher quality, CRT display iii) better mouse, printer, and so on. For example, the user merely pushes the notebook 6 into the docking station 7 quickly and easily, and all peripherals are then hooked up, without any further user hookup activity. Another area of advantage C) the docking station 7 provides a platform by which users can retrofit ISA or EISA add-in cards from a previous installation and obtain their use with the notebook 6. In FIGS. 5, 6, and 7 7 (which detail the system 100 in FIGS. 3 and 4) a block diagram of a first part of a preferred embodiment computer system 100 shows in FIG. 5 a single-chip microprocessor unit MPU 102 connected to a 32-bit bus 104, DRAM (dynamic random access memory) 106, FPU (floating point unit) 108, single-chip peripheral control unit PCU 112, single-chip peripheral processor unit PPU 110 (in FIG.6) and a display controller 114 (in FIG. 7). The FPU 108 of FIG. 5 is suitably either implemented on a separate chip as shown, or integrated onto the same chip as MPU 102 in, for example, a 486DX chip, a 586-level microprocessor, or a superscalar or multi-processor of any type. In FIG. 6, PPU 110 has terminals connected via an 8-bit bus 116 to a keyboard controller and scan chip KBC/SCAN 118, BIOS (basic input/output system) ROM (read only memory) 120, HDD (hard disk drive) unit 122, and logic chip 124. PPU 110 has further terminals connected to a floppy disk drive (FDD) 126, a printer port EPP/ECF 128 to a printer 129, and two serial input/output ports SIO 130 and 132. A temperature sensor 140, or heating sensor, is connected via logic 124 to the rest of the system to signal temperature levels and cooperate in the power management of the system. KBC/SCAN 118 is connected to a computer keyboard 142 and computer mouse input device 144. BIOS ROM 120 is addressed by 18-bit addresses by signals from MSB (most significant bits) or LSB (least significant bits) 16-bit halves of bus 104 via a multiplexer (MUX) 150. Also BIOS ROM is addressed via 16 bit addresses built up by successive 8-bit entries from bus 116 in two cascaded 8-bit registers 152 and 154. In this way, separate PPU 110 pins for BIOS ROM addresses are advantageously rendered unnecessary. An audio sound system 160 is connected to PPU 110, thereby providing sound resources for the system 100. A power switch circuit 170 responsive to a SUSPEND# line from PPU 110 controls the supply of power from a power supply 172 to system 100 via three pairs of lines A, B, C from power switch 170 to supply voltages VPP and VCC to system 100. Power supply 172 is energized by an electrical battery 176 and/or an external power source 174. A clock switch control circuit 180 (FIG. 5) supplies clock signals for system 100 via a line CLK of bus 104. Returning to FIG. 5, 4 banks of DRAM 106 are resistively connected to MPU 102 via 13 memory address MA lines, 8 CAS (column address strobe) lines, four RAS (row address strobe) lines, and a WE (write enable) line. 32 memory data MD lines provide a path for data to and from DRAM 106 between MPU 102 and DRAM 106. A frequency-determining quartz crystal 182 of illustratively 50 MHz (MegaHertz) is connected to MPU 102. A 32 KHz (kiloHertz) output terminal from PPU 110 is connected resistively to display controller 114. In FIG. 7, display controller 114 is connected directly to an LCD (liquid crystal display) or active matrix display of monochrome or full color construction. Display controller 114 is connected via a CRT (cathode ray tube) interface (I/F) 192 to a CRT computer monitor 194. A blanking adjustment control 196 is connected to display controller 114. A frame buffer 202 is connected to display controller 114 via address, data and control lines. Two sections A and B of display DRAM 204 and 206 are also connected to display controller 114 via their own address, data and control lines. Additional bus master devices 210, such as LAN (local area network) and SCSI (Small Computer System Interface) are connected to bus 104 in system 100. Also, slave devices 220 connect to bus 104. FIG. 8 is a plan view of a preferred embodiment apparatus having a multiple layer (e.g. 10-layer) printed-wiring board 302 and electronic components of the computer system 100 of FIGS. 5-7. FIG. 8 shows a component side of printed wiring board 302, while a solder side of board 302 lies opposite (not shown) from the component side. Arranged at vertices of a centrally located quadrilateral 303, and interiorly disposed on the component side of board 302, are the MPU 102, PPU 110, PCU 112 and video, or display, controller 114. All these component devices 102, 110, 112 and 114 are on a high speed bus 104, and because the quadrilateral affords an arrangement whereby these devices are located very close to each, the high speed bus 104 is advantageously made physically small and compact both for small physical size and low electromagnetic interference due to small electrical size. Near the PCU 112 and near a corner 304 of board 302 lies a PCMCIA card, such as flash memory card, connector 306. At the system level, system 100 as implemented in the embodiment of FIG. 8 has a main microprocessor integrated circuit 102, a card interface integrated circuit 112, a peripheral processor integrated circuit 110, a display controller integrated circuit 114, and a bus 104 on the printed wiring board interconnecting each of the integrated circuits 102, 112, 110, and 114. The integrated circuits 102, 112, 110 and 114 establish corners of a quadrilateral 303 bounding the bus 104. Further provided are a plurality of external bus connectors disposed in parallel outside quadrilateral 303 and connected to bus 104. A clock chip AC244 (180) is approximately centrally located inside quadrilateral 303 and connected via approximately equal-length lines to each of the integrated circuits 102, 112, 110 and 114 thereby minimizing clock skew. Four long DRAM 106 SIMM (single inline memory module) socket connectors for banks 0-3 lie parallel to each other, parallel to a short side 308 of board 302, and perpendicular to the connector 306. FPU 108 is located adjacent to one of the DRAM connectors near the MPU 102. SIMM sockets for the DRAMs provide a direct path for the wiring traces on the printed wiring board 302. Along a longer side 310 of board 302 lie LED connectors D5 and D6 and a loudspeaker connector J33. Next to the holder for battery B1 are connectors J17 for mouse 144 and J18 for keyboard 142. A power supply unit 172 located on the edge of side 310 lies near a corner 312 diagonally opposite corner 304. A second short side 314 lies opposite side 308 of board 302. At the edge of side 314 are located two power connectors J36 and J37, a serial connector J22 and a parallel port connector J38 designated "Zippy." Looking interiorly, betweem side 314 and PPU 110 and parallel to short side 314 are a floppy disk drive connector J19 located closely parallel to a hard disk drive connector J21. A second long side 316 lies opposite side 310 of board 302. At the edge of side 316 and centrally located are a 15 pin connector J11 parallel to a 20 x 2 pin header J12. A video connector J13 lies next to J12 below quadrilateral 303. Between video controller 114 and PCU 112 lie three TMS45160 chips disposed parallel to each other and to side 316 and substantially parallel to the side of quadrilateral 303 defined by vertices 114 and 112. Next to video controller 114 outside quadrilateral 303 lie three bus 104 connectors J14, J15, J16 parallel to each other and to long side 316. FPGA 124 is located above PPU 110 between PPU 110 and side 310 near power supply 172. A DOS-compatible static 486 core in MPU 102 allows on-the-fly clock-scale and clock-stop operation to conserve battery power. The special clocking scheme allows optional clock stopping between keystrokes. Low voltage operation such as 3.3 volts or less, coupled with power management, provides the capability to achieve low system battery power consumption. Bus 104 is a high speed high bandwidth bus to improve data transfers of bandwidth-intensive I/O devices such as video. Electrical noise is minimized by this embodiment which has short conductor trace lengths and direct point-to-point clock traces. Each clock trace has a series or parallel termination to prevent undesirable reflections. An economical 74LS244 clock driver 180 is provided in the interior of quadrilateral 303. Placement of that clock driver 180 is such that the length of the clock traces therefrom to each chip 110, 102, 114 and 112 are approximately equal, advantageously minimizing clock skew. Integrated card controller PCU 112 can be configured to support a portable peripheral bus such as PCMCIA (Personal Computer Memory Card International Association), for example. The connector 306 near corner 304 has one card insertion level in a plane on the top side of board 302 and a second card insertion level in a plane on the underside of board 302. Single 8-bit ROM 120 support allows for integration of the system BIOS and video BIOS into the same device to reduce motherboard real estate and reduce cost. MPU 102, PPU 110 and PCU 112 are highly integrated into three 208 pin PQFP devices (see FIG. 58 later hereinbelow) which reduces board space and reduces active battery power consumption by integrating all CPU and system logic. In other embodiments, the PPU 110 and PCU 112 are integrated together into two devices. In still other embodiments the MPU 102, PPU 110 and PCU 112 are integrated into only one single-chip device. However, the three chip embodiment shown, with its substantially equal pin numbers, provides remarkable economy and board layout convenience. In the three-chip embodiment illustrated in FIGS. 5-7, the chips are manufactured using submicron process technology to illustratively provide operation up to 66 MHz and higher at 3.3 volts while keeping power consumption and heat dissipation remarkably low. Returning to FIG. 8, physical strength and reasonable rigidity without fragility are provided by the relaively small size of board 302. Additional mounting holes near connectors for bus 104 are provided. Board 302 is firmly mounted with screws, bolts, rivets or other mounting elements in an enclosure 325 associated with or comprised by base 22 of FIG. 1. When an external connection to bus 104 is made, such as in a docking station or other environment, the mounting elements in the additional mounting holes advantageously provide substantial load-bearing support strength for improved reliability. In FIG. 9 microprocessor unit (MPU) 102 comprises a preferred embodiment device illustrated in block diagram form. MPU 102 integrates a 486-class CPU (central processing unit) 701 which has a CPU core 702, an 8K-byte write-through 32-bit instruction/data cache 704, and a clock, PLL (phase-lock loop), and control circuit 706. CPU core 702 is described in the TI 486 Microprocessor; Reference Guide , 1993. Cache 704 is two-way set associative and is organized as 1024 sets each containing 2 lines of 4 bytes each. The cache contributes to the overall performance by quickly supplying instructions and data to an internal execution pipeline. A power management block 708 provides a dramatic reduction in current consumption when the microprocessor MPU 102 is in standby mode. Standby mode is entered either by a hardware action in unit 920 of PPU 110 or by a software initiated action. Standby mode allows for CPU clock modulation, thus reducing power consumption. MPU power consumption can be further reduced by generating suspend mode and stopping the external clock input. The MPU 102 is suitably a static device wherein no internal data is lost when the clock input is stopped or clock-modulated by turning the clock off and on repeatedly. In one preferred embodiment, without suggesting any limitation in the broad range of embodiments, the core is a three volt, 0.8 micron integrated circuit having clock operation at 50 or 66 MHz., with clock doubling. Core 702 has a system-management mode with an additional interrupt and a separate address space that is suitably used for system power management or software transparent emulation of I/O (input/output) peripherals. This separate address space is also accessible by the operating system or applications. The system management mode is entered using a system management interrupt which has a higher priority than any other interrupt and is maskable. While running in the separate address space, the system management interrupt routine advantageously executes without interfering with the operating system or application programs. After reception of the system management interrupt, portions of the CPU are automatically saved, system management mode is entered and program execution begins in the separate address space. System management mode memory mapping into main DRAM memory is supported. The MPU 102 has interface logic 710 which communicates via external FPU/IF terminals to FPU 108 when the latter is present. System configuration registers 712 are accessible via a CPU local bus 714. Bus 714 is connected to CPU 701, to a bus bridge circuit 716, and to a DRAM memory controller (MCU) 718. Registers 712 also are bidirectionally connected to the bus bridge circuit 716 via line 722. DRAM memory controller 718 is connected to system configuration registers 712 via line 721 and receives signals via a line 724 from bus bridge 716. DRAM memory controller 718 supplies DRAM addresses and DRAM control signals to external terminals of single-chip MPU 102. DRAM memory controller 718 is connected by handshake line 727 to power management circuit 708, which circuit 708 is also connected by line 726 to bus bridge 716 and by line 728 to clock, phase lock loop and control circuit 706. A data circuit 720 provides a data router and data buffers. DRAM memory controller 718 supplies signals to circuit 720 via line 732. Data circuit 720 also bidirectionally communicates with bus bridge 716 via Line 730. Data circuit 720 reads and writes DRAM data to external terminals on data bus 734. Main bus 104 connects via terminals to MPU 102 and connects via paths 736 and 738 to data circuit 720 and bus bridge 716 respectively. Data circuit 720 includes two-level posted DRAM write buffers, an integrated four-level DRAM refresh queue, and provides for three programmable write-protection regions. DRAM memory controller 718 supports up to 256 megabytes or more of DRAM memory with up to four or more 32-bit banks without external buffering. For example, DRAMS of 256K, 512K, 1M, 2M, 4M, 8M, and 16M asymmetric and symmetric DRAMS and up to 64M and higher DRAMS are readily supported. Shadowed RAM is supported. Additionally, the memory interface buffers can be programmed to operate at different operating voltages such as 3.3 or 5.0 volts for different types of DRAMS. The DRAM memory controller 718 is programmable to support different access times such 60 or 80 nanoseconds (ns). For example, 60 ns. is quite advantageous at 50 and 66 MHz. clock speeds at 3.3 v. Varous refresh modes are programmably supported, such as slow, self, suspend, and CAS-before-RAS refresh. Maximum memory throughput occurs because DRAM parameters are driven off the internal high-speed 50/66MHz. CPU clock to improve resolution, thus taking full advantage of the integration of the DRAM controller. The bus bridge 716 acts as an integrated interface which is made compliant with whatever suitable specification is desired of bus 104. Bus bridge 716 advantageously acts, for example, as a bus master when there is a MPU 102 initiated transfer between the CPU and bus 104, and as a target for transfers initiated from bus 104. A bus-quiet mode advantageously supports power management. The bus-quiet mode is used to inhibit cycles on bus 104 when the CPU is accessing the DRAM 106 or internal cache 704. Put another way, bus quieting reduces system power consumption by toggling the data/address bus 104 only on bus transfers. Bus quieting is not only implemented on MCU 718 but also PPU 110 bus bridge 901 and KC/IDE block 934. All signals, buses and pins are made to change state only when they need to. For example, each data bus flip-flop holds its state until the next change of state. As thus described, MPU 102 integrates in a single chip a 486-class CPU, a DRAM controller, and a bus interface in any suitable integrated circuit package, of which one example is 208 pin PQFP (plastic quad flat pack). PPU 110 and PCU 112 also partition system functionality into respective single-chip solutions which can have the same type of package as the MPU 102, such as plastic package. These latter two chips can even be pinned out in a preferred embodiment from the same 208 pin PQFP package type. In FIG. 10 a preferred embodiment layout for MPU 102 has an improved topography wherein MPU 102 is realized as an integrated circuit die with a single substrate 802 with approximately 1:1 ratio of side lengths. Various circuit regions or blocks are fabricated on substrate 802 by a CMOS (complementary metal oxide semiconductor) process. Other processes such as BiCMOS (bipolar CMOS) can also be used. The 486 CPU core 702 is located in one corner of the die to provide maximum accessibility pin-out with short conductor length to bond pads 804 on the nearby margins forming a right angle at the corner 806 of the substrate 802. Cache 704 lies closely adjacent to CPU core 702 for high speed CPU access to the cache. The memory controller 718 MCU is laid out together in an approximately rectangular block of circuitry lying along a strip parallel to cache 704, and perpendicular to microcode ROM and core 702 along substantially most of an edge of the chip 802 opposite to an edge occupied by cache 704. In this way cache 704 and MCU 718 bracket core 702. On a side 818 opposite microcode ROM of core 702 lies bus bridge 716 laid out in a long strip parallel and stretching most of the length of side 818. Advantageously, the long length of this bus interface 820 provides physical width accessibility to the numerous terminals for connection to the wide bus 104 of system 100 of FIGS. 3-7. In FIG. 11 PPU 110 provides a single-chip solution that has numerous on-chip blocks on chip 901. First is a bus interface 902 to interface from external bus 104 to an on-chip bus 904. Bus interface 902 is compatible with bus 104 externally, and is at the same time also compatible with bus 904 as a fast internal bus for integration of several peripherals described hereinbelow. For example, the peripherals in various embodiments suitably provide peripheral functions compatible with the IBM-compatible "AT" computers, or compatible with Apple "Macintosh" computers or peripherals having any desired functionality and operational definition as the skilled worker establishes. Bus interface 902 has advantageously short bus 104 ownership when mastering to minimize overall system 100 latency. Bus interface 902 provides fast DMA (direct memory access) transfers from internal I/O devices to agents (circuits) on bus 104. Bus interface 902 performs a disconnection with retry operation for slow internal accesses to reduce the latency still futher. Illustrative bus 104 frequency is 33 MHz. at either 5 volts or 3.3 volts, although other lower or higher frequencies and voltages are also suitably established in other embodiments. In the embodiment of FIG. 11 the internal bus 904 is suitably clocked at half or a quarter of the bus 104 frequency, and higher or lower frequency relationships are also contemplated. A bus arbiter 906 on-chip provides arbitration of bus 104 for the MPU 102 of FIG. 5, PPU 110 of FIG. 6, and two external bus masters 210 of FIG. 7. PPU 110 acts as a bus 104 bus master during DMA cycles for transfers between bus 104 and a DMA peripheral 910. One preferred embodiment provides more peripherals that are compatible with the "PC-AT" architecture. Since the bus 904 provides an on-chip common connection to all of these on-chip peripherals, their speed and other electrical performance are enhanced. For example, two DMA controllers 910 control the DMA transfers through bus interface 902. In PPU 110 DMA controllers 910 are connected to bus 904 and separately also to both bus arbiter 906 and bus interface 902 via path 911. DMA controllers 910 also pin out externally to four pins from bond pads 912 on chip 901. Two interrupt controllers 914 provide channels individually programmable to level-triggered or edge-triggered mode. Also in interrupt controllers 914 is an interrupt router that routes an external interrupt from bus 104 or an interrupt from PCU 112 to a software-selectable interrupt channel. In PPU 110 interrupt controllers 914 and a timer/counter 916 connect to bus 104 and also pin out externally to 9 pins and 2 pins respectively. An RTC (real time clock) circuit block 918 has an integrated low-power 32 kHz. oscillator and a 128 byte CMOS SRAM (static RAM). Examples of some features and circuitry which are useful in DMA controllers 910, interrupt controllers 914, timer-counter 916 and RTC circuit 918 are found, respectively, in a commercially available 8237, 8259, 8254 and MC146818 device together with improvements as described herein. It is also contemplated that still other peripherals be provided on-chip for system purposes as desired. A power management block 920 has a battery powered first section 920A for operation whenever the system 100 is energized, and a section 920B which is battery powered at all times. Power management block 920 provides clock control for CPU 702 even without a system management interrupt. Mixed voltage (e.g., 3.3v/5v) support is provided as a power management function. Power management block 920 includes system activity timers named the STANDBY timer and the SUSPEND timer which monitor bus 104 activity via DEVSEL# signal, display frame buffer (e.g., VGA) activity (see controller 114 and frame buffer 202), DMA requests, serial port 130 interrupts and chip selects via a COM1 signal, parallel-port 128 interrupts and chip select via a LPT1 signal, hard disk controller 122 interrupts and chip select, floppy disk controller 126 interrupts and chip select, programmable chip select signals PCS0# and PCS1#, and other interrupts IRQ9, IRQ10, IRQ11 and IRQ15. Power management block 920 further provides for short term CPU clock speedup timer monitoring of keyboard 142 and mouse 144 interrupt requests from KBC/SCAN chip 118, as well as bus 104 bus master cycle requests, and masked system activity timer output. CPU clock masking, or clock-modulation, is provided by power management block 920 hardware that includes a programmable register for adjusting the gate-on-to-gate-off ratio, i.e., a ratio of clock time on to clock time off. A bidirectional system management interrupt handshaking protocol is supported by power management block 920. Also, six power management traps are provided for IDE block 122, FDD 126, serial port 130 COM1, parallel port 128 LPT1, and the programmable chip selects PCS0# and PCS1#. Four-bit (16 level) backlight intensity adjustment pulse-width modulation (PWM) advantageously results from the operations of power management block 920 in response to intensity control 34 of FIG. 1. When power management block 920 has caused substantial sections of PPU110 and the rest of system 102 to be deactivated, reactivation can be initiated by circuitry in block 920 responsive to an RTC alarm, a modem ring, a suspend/resume button, keyboard IRQ (interrupt request), mouse IRQ, ON/OFF button, a card system management interrupt CRDSMI from PCU 112, or a low-to-high transition on a battery input BATLOW. Shadow registers in power management block 920 support saving the full system state to disk. Bus quieting and I/O leakage current control circuitry are also included in power management block 920. Advanced Power Management support is also provided by power management block 920. Further in FIG. 11, a floppy disk controller block 930, digital disk controller (FDS), hard disk interface XD/IDE 934, serial interface block SIU 936, and a parallel port interface 983 are all coupled to internal bus 904 and to pins externally. The floppy disk controller block 930 is integrated on-chip in PPU 110 to support 3.5 inch drives (720 kB (kilobyte), 1.44 MB (megabyte), and 2.88 MB) as well as 5.25 inch drives (360 kB and 1.2 MB). All buffers are integrated. Floppy disk controller block 230 has circuitry to accommodate data in several track formats: IBM System 34 format, perpendicular 500 kb/s (kilobits per second) format, and perpendicular 1-Mb/s (one megabit per second) format. A data FIFO (first-in-first-out) buffer operates during the execution phase of a read or write command in block 930. Block 930 also has a 255-step (16 bit) recalibrate command and function. This floppy disk controller block 930 can be reset by software. It has an integrated floppy data separator with no external components in this embodiment. Drive interface signals can be multiplexed to parallel port 938 pins for use with an external drive. The interface 934 provides a complete IDE hard disk interface logic with high speed access. The IDE hard disk is isolated and can be powered off independently. Also included in interface 934 is a bus interface for XD bus 116 of FIG. 6, which supports BIOS ROM (which can be flash EEPROM electrically erasable programmable read only memory), provides keyboard controller KBC/SCAN connections, has two user-programmable chip selects, and can connect to audio CODEC (coder-decoder). Further in FIG. 11 a block for miscellaneous control functions is provided as block 940. Serial interfaces 936A and 936B each have a 16-byte FIFO for queuing and buffering the serial data to be transmitted and received, and has a selectable timing reference clock of 1.8461 MHz. or 8 MHz. Parallel interface 938 has a 16-byte datapath FIFO buffer and provides DMA transfer. Support for fast parallel protocols such as ECP and EPP is suitably provided. More than one floppy disk drive FDD 126.0 and 126.1 are suitably accommodated by provision of a multiplexer 939 to mux the output of digital floppy disk controller 932 with parallel port 938. When a control signal PIFFDC from configuration registers 1222 of PPU 110 causes mux 939 to select floppy disk, then external pins otherwise utilized by parallel port 938 are suitably used instead for a FDD 126.1. In FIG. 12 a preferred embodiment layout for PPU 110 has an improved topography wherein PPU 110 is realized as an integrated circuit die 901 with a single substrate having approximately 1:1 ratio of side lengths. Various circuit regions or blocks are fabricated on die 901 by a CMOS (complementary metal oxide semiconductor) process. Other processes such as BiCMOS (bipolar CMOS) can also be used. On a side 1002 lies bus arbiter 906 and bus interface 902 all laid out in a long strip 1004 parallel and stretching most of the length of side 1002. Advantageously, the long length of this circuitry strip 1004 provides physical width accessibility to numerous terminals for connection to the wide bus 104 of system 100 of FIGS. 5-7. Adjacent and perpendicular to circuitry strip 1004, blocks 936, 938 form a column 1006 which occupies more than half of the length of a side 1008. Perpendicular to column 1006 lies a wide strip for floppy disk controller 932 and hard disk interface 934A laid out parallel to and on the opposite side 1010 from side 1002 PCI/AT bus interface strip 1004. The XD bus interface portion of circuit 934 also lies on side 1010. RTC 918 with its RAM 919 lies at a corner of the die on side 1010 atop a column 1012 of PMU 920 circuitry occupying a strip perpendicular to both the edge 1010 with FDC/IDE I/F and to edge 1002 with bus bridge 1004. Battery powered PMU RTC 920B lies adjacent to RTC 918 in said corner in a 3.3 volt well, or region, distinct from all the rest of chip 901 which is powered at a different power supply voltage VCC such as 5 volts. A large, substantially rectangular or square central region of die 901 is occupied by the DMA 910, interrupt circuitry 914, timer/counters 916, and dynamic clocking circuitry described elsewhere. The central location of these circuits minimizes clock skew, and promotes efficient layout of fast-AT internal bus 904 around this central region. Not only configuration registers 1222 but also local block registers are efficiently grouped together in a central block named Registers in FIG. 12 between the central block 910, 914, 916 and the strip 1004. Also, bus 904 is internally adjacent to and within the surrounding strips 1004, 1006, 934, 932, and 1012. The latter strips are advantageously located next to the external pins they heavily employ. In FIG. 13, returning to system level to consider a further important system embodiment utilizing the special chips therein, a computer system 400 of a preferred embodiment has an enclosure 402 with a printed wiring board holding components chosen, configured and combined for advantageous desk top computer or portable (e.g. notebook) application. MPU 102 is coupled to FPU 108 and additionally coupled to a DRAM memory 406. A main bus 104 interconnects MPU 102, PPU 110, VGA/LCD display controller chip 114, PCU 112 and a LAN (local area network) controller 410. LAN controller 410 suitably supports either Ethernet protocol via coax path 412, or token ring protocol via path 414 to stations 400.1, 400.2,...400.n, or both protocols, using TMS380 LAN technology from Texas Instruments Inc. PPU 110 has flash ROM 120 connected to some terminals thereof. This optional flash BIOS allows user upgradeable BIOS support. At other terminals is connected a keyboard controller 118 which in turn is connected to both a keyboard 142 and a mouse 144. PPU 110 is further connected to a hard disk drive 122 and a floppy disk drive 126 with insertable magnetic floppy disks. PPU 110 further interfaces to a printer 129. Display controller chip 420 is externally connected to a CRT 190 or alternatively to a display panel such as one using digital micromirror devices or field emission device flat panel technology from Texas Instruments Incorporated. PCU 112 is externally connected to flash memory cards 412. These cards in one embodiment are 3 or 5 volt PCMCIA cards. A modem 430 is connected to a serial port of the PPU 110 in system 400. Modem 430 connects to the telephone network either by direct connection by a rear jack on enclosure 402, or by a wireless interface incorporated in the system. Modem 430 can also be implemented by using a PCMCIA modem card 432 insertable into card socket 433 for PCU 112. Modem card 432 connects to a DAA interface 434 to telephone line 436. An infrared interface 440 connects to another serial port of the PPU 110 and connects to an emitter/detector assembly 38 having emitter LED 452 and photodetector diode 454. Bus 104 in one embodiment can be a PCI (Peripheral Component Interconnect) bus which is described in a published PCI Specification 2.0 from PCISIG (PCI Special Interest Group). A power supply 464 for connection to AC power with or without battery backup provides supply voltage to energize the PPU 110 and the other circuits in system 400. In FIGS. 14 and 15 the description turns to further specifics of circuits in the PPU 110 embodiment. Bus interface 902 of FIGS. 11 and 14 is connected between bus 104 and internal bus 904 of PPU 110. A bus master 1202 bidirectionally connected via lines 1203 to bus 104 has state machines and interface logic used when the arbiter 906 of FIGS. 11 and 15 grants control of bus 104. A slave block 1204 bidirectionally connected via lines 1205 to bus 104 translates bus cycles externally initiated on bus 104. The slave block 1204 translates these bus cycles to an internal bus controller block 1206 to which slave block 1204 is bidirectionally connected via lines 1207. Slave block 1204 does non-posted writes and wait-stated reads. Internal bus controller 1206 generates the signals for communication on the internal bus 904 via bidirectional lines 1209. A data router/buffer 1210 has latches for data latching between bus 104 and internal bus 904 via bidirectional lines 1213 to bus 104 and bidirectional lines 1215 to internal bus 904. Respective controls from internal bus controller 1206, slave 1204 and bus master 1202 pass via respective lines 1217, 1219 and 1221 to data router/buffer 1210. Internal bus controller 1206 controls assembly and disassembly of data between the internal bus 904 and the data router/buffer 1210. Registers CFG 1222 specify the configuration of interface 902, and receive information from slave 1204 via a line 1225 and are bidirectionally connected via lines 1227 to data router/buffer 1210. Bus master 1202 is bidirectionally connected to internal bus controller 1206 via lines 1229. Bus master 1202 is bidirectionally connected to slave 1204 via lines 1231. Internal bus controller 1206 provides subtractive decode DEVSEL# assertion. Address decoding for slave devices connected to the internal bus 904 is performed by those devices. In FIG. 15 DMA circuitry in PPU 110 is shown in more detail. Bus arbiter 906 receives bus request signals from bus 104 via two pins REQ0# and REQ1#, and supplies bus grant signals to bus 104 via two pins GNT0# and GNT1#. Since bus master 1204 in bus interface 902 is on-chip in the PPU 110, the arbiter 906 has two more lines REQ2# and GNT2# internally connecting to bus master 1204. Arbiter 906 also has an input line HLDA/MPUREQ# (Hold Acknowledge high, MPU 102 Request low, CPU acknowledges it has gotten off bus 104) and an output line HOLD/MPUGNT# (Hold high/ MPU 102 Grant low, arbiter 906 request to CPU that CPU get off bus 104). HLDA is a grant of both bus 904 and bus 104 for DMA operation by DMA controller 910. Internal bus control 1206 supplies a bus idle signal IDMAGNT# (internal bus DMA grant, active low) to slave block 1202. DMA controller 910 supplies a DMA controller request HREQ to both the internal bus control 1206 and the slave block 1202 via a line 1303. Slave block 1202 acknowledges with signal IHLDA to both DMA controller 910 and internal bus control 1206 on a line 1305. Internal bus 904 interconnects internal bus control 1206, DMA controller 910 and first and second DMA devices 1310 and 1312. Respective signals and lines are provided for DMA devices 1310, 1312 requests DREQ1, DREQ2 to DMA controller 910, and DMA device grants DACK1, DACK2 from DMA controller 910 back to DMA devices 1310, 1312. Note that FIGS. 14 and 15 should be read together for both the data and control paths. In FIG. 16 a BIOS addressing circuit interconnects the PPU 110 of FIG. 6 with BIOS flash EEPROM 120 when flash is used. The XD bus interface in PPU 110 is suitably connected to the BIOS ROM 120, keyboard controller KBC/SCAN 118, and additional devices such as audio codec chip 160. BIOS flash memory 120 is connected to PPU 120 is thus supplied with address bits XA(1:0), a chip select ROMCS#, a read strobe XDRD# and a write strobe XDWR#. An upper set of 15 address lines are driven onto the bus 104 by PPU 110 while PPU 110 is waiting for data to be returned from the BIOS memory 120 with the resulting advantage that no external address latches are required. When BIOS memory 120 is flash, two 8-bit latches 152 and 154 are used to latch the BIOS address, and a latch enable signal EEACLK is provided from a pin of PPU 110 to clock inputs of both of the latches 152, 154 to clock the latches. As shown in FIG. 16, the 8-bit XD bus is connected directly to data terminals of BIOS memory 120 and of data D inputs of 8-bit latch 152. Latch 152 has its Q output lines connected to 8 MSB bits AD(17:10) of BIOS memory 120, and latch 152 has the same Q output lines also connected to the data D inputs of 8-bit latch 154. Latch 154 has its Q output lines connected to 8 LSB bits AD(9:2) of BIOS memory 120. Thus, these latches have an advantageously bus-wide serial structure in the addressing of BIOS 120. In FIG. 17 the PPU 110 of FIGS. 6 and 11 is connected with BIOS ROM 120, KBC (Keyboard Controller) 118, and IDE Drive 122. Control and data connections and signals provide in FIG. 17 further detail to FIG. 6. The XD bus 116 of FIGS. 6 and 17 has associated control signals which are split into respective sections 1501 and 1502 for XD and IDE interface signals. These sections 1501 and 1502 have separate voltage rails in PPU 110 connected to power supply lines at pins VCC_XD and VCC_DK of PPU 110, see FIG. 32. The structural feature and method of separate voltage rails in a preferred embodiment provides advantageous flexibility in system configuration, For example, a keyboard controller KBC/SCAN 118 and BIOS ROM, both of 3.3 volt type selected for low power consumption, are suitably combined in system 102 with an IDE disk drive 122 selected to be of 5 volt type for low cost. Eight outgoing control signal lines 1515 and three incoming control signal lines 1517 in FIG. 15 show the PPU 110 pin connections to IDE Drive 122 as detail to FIG. 2. An eight-bit buffer 1510 (such as a '245 chip) responsive to PPU 110 control line IDEIOR# (and powered from supply voltage VCC) couples the XD bus 116 to the lower eight lines DD(7:0) of IDE drive 122, while the upper 8 lines DD(15:8) are fed directly from the DD pins of PPU 110. Six outgoing control signal lines 1523 and two incoming signal lines 1521 in FIG. 17 show the PPU 110 pin connections to KBC 118 as further detail to FIG. 6. Chip select and selectable clock signals are provided for KBC 118, and read/write strobes and 8-bit data signals are analogous to the signals for other XD-bus peripherals of FIG. 17. Address line XA1 functions as and connects to input A2 of KBC 118. The XRD# and XWR# signals serve as read and write strobes for both memory and I/O cycles. When ROM chip select ROMCS# is active, XRD# and XWR# are equivalent to the internal memory read MEMR# dnd memory write MEMW# signals; for all other accesses, XRD# and XWR# are equivalent to the internal I/O read IOR# and I/O write IOW# signals. Referring to lines 1531 of FIG. 17, two DMA channels and a programmable chip select PCS0# are available to support a business audio chip such as the AD1848 commercially available from Analog Devices Inc. A second programmable chip select PCS1# is also available. When a ROM (and not flash memory) is used to realize BIOS ROM 120, connections are made from PPU 110 as shown in FIG. 15 to the control pins of ROM 120. A buffer 150 couples 16 lines such as AD(17:2) from bus 104 to address inputs A(17:2) of ROM 120. The other AD lines are used to create a separate address space for an additional ROM or ROMs in an alternative embodiment. In FIG. 18 the description to turns to the card interface chip PCU 112 of FIG. 5. PCU 112 has bus interface 1602 connected to bus 104. Bus interface 1602 is further connected to two illustratively identical card interface circuits 1610 and 1612 for card slots A and B. Configuration registers 1616 bidirectionally communicate with bus interface 1602 by lines and supply configuration information CFG to circuits 1610 and 1612 and well as to blocks 1620 and 1630 for Interrupt, power management circuitry and other logic. Cards are advantageously insertable and removable while power to PCU 112 is on due to integrated hot insertion and removal buffers in circuits 1610 and 1612. Plural selectable supply voltages (e.g., 3.3v and 5 v) are supported. The card controller generates control signals for individual slot power control to connect the selected supply voltage to each card under software control. In one embodiment the card controller is made register compatible with a controller 82365SL DF exchangeable card architecture commercially available from Intel Corporation. PCU 112 can be replicated on bus 104 thereby providing numerous card slots as desired for a particular application system. The pinout of PCU 112 is described in detail elsewhere herein. In brief, the card data path CDATA (A or B) is 16 bits wide. Each circuit 1610 or 1612 respectively assembles or concatenates 8-bit or 16-bit card accesses from its CDATA lines into 32-bit words onto bus 104 lines AD(31:0) via the bus interface 1602. Circuit 1620 bidirectionally communicates with circuits 1610 and 1612 via lines 1611 and 1613 respectively. Bus interface 1602 has bus 104 connections to lines AD(31:0), input controls CTRLIN and output controls CTRLOUT. Each of circuits 1610 and 1612 has respectively A- and B-designated 26 CADR address lines, 16 bidirectional data lines CDATA and 20 control lines. Bus interface 1602 via a data router circuit 1615 connects in parallel to both circuits 1610 and 1612 via 26 ADR address lines, 32 DATA lines (data is in assembled form) and by lines marked control. Pins IRQn differ in number n with the particular embodiment of PCU 112. For example, in systems having an externally accessible ISA bus, 10 pins IRQn are provided in a first embodiment with interrupts routed to the appropriate IRQn line depending on the card function. In systems having an ISA bus internal to PPU 110 only, only three pins IRQ named CRDAIORQ, CRDBIORQ, CRDSRVRQ are provided in a second embodiment with interrupts routed by special shadowing in PPU 110 to the appropriate IRQ line among typically 10 ISA interrupt lines, depending on the card function. The second embodiment has economic and speed advantages. In a third embodiment of PCU 112, ten pins IRQn for routed interrupts muxed with CRDAIORQ, CRDBIORQ, CRDSRVRQ are provided, so that the chip may be used in either an externally accessible ISA bus environment, or the PPU 110 internal bus environment depending on the system manufacturer choices incorporating the PCU 112. The description of FIGS. 38 and 43 herein provides further description of the shadowing circuitry, systems and methods of this third embodiment. In FIG. 19 PCU 112 in a preferred embodiment has genarally rectangular integrated circuit blocks fitted together in a layout comprising two columnar halves 1705 and 1707 on an approximately 1:1 square die 1710 having I/O buffers and small rectangular bond pads 1715 located on a narrow peripheral strip 1720 around the perimeter of the die 1710. Pin references 208, 1 are provided in the lower left corner of FIG. 19. In FIG. 19, bus interface 1602 has PCI I/O and PCI Controller blocks oriented at upper center in the layout. In the upper left corner lies the Control circuitry 1620, 1630 with access to the IRQ pins and SMI pin nearby. Configuration Registers 1616 occupy about half the area of column 1705 and are flanked by Address Decode A and Address Decode B circuitry for controllers 1610 and 1612 respectively. Column 1707 controller 1610 blocks for FIFO A and PCMCIA controller A occupy the upper half of column 1707, and controller 1612 blocks for FIFO B and PCMCIA controller B occupy the lower half. The A circuitry in the upper half is advantageously rotated in orientation by an angle of 90 degrees relative to the B circuitry in the lower half to form two quadrants of circuitry with high bond pad accessibility. The FIFO A (first-in-first-out buffer) in circuit 1610 of FIG. 19 occupies a rectangular region spanning the top of column 1707, and FIFO B lies in the lower right next to the corner at the bottom of column 1707. PCMCIA controller block A in controller 1610 lies adjacent to FIFO A. PCMCIA controller block B in controller 1612 lies adjacent to FIFO B and perpendicular in aspect to PCMCIA controller A. In this way, circuits which have many external inputs and outputs like FIG. 18 circuits 1602C (AD pins), 1610 (A_CA and A_CDATA pins) and 1612 (B_CA and B_CDATA pins) also have substantial bond pad physical accessibility, as shown in FIGS. 19 and 57. Data router 1615 lies in a narrow peripheral strip adjacent to PCMCIA controller A and between FIFOs A and B. Comparing FIGS. 18 and 19, data router 1615 advantageously supplies and routes the Controller A and B Configuration, Address, Control and Data information from block 1602 as intended by the information in Configuration Registers 1616. In FIG. 18 block 1615, the interior joinings of A and B lines are representative of muxes or other selector and routing logic to complete the information paths. In FIG. 20, PPU 110 power control output pins for hard disk HDDPWR#, floppy disk FDDPWR# and programmable chip select PCSPWR# are connected to respective MOSFETs (metal oxide semiconductor field effect transistors) 1822, 1824 and 1826, or any other suitable power control elements) so that a selected supply voltage such as 3 volts or 5 volts is controllably applied to or disconnected from the corresponding peripheral HDD 122, FDD 126 and PCS chip such as modem and audio, for advantageous system power management. In other words, each peripheral has its own individual supply voltage wherein one peripheral can run on a switchable 5 volts for low cost, and another peripheral can run on a switchable 3 volts for low power. Another power control output pin SIUPWR# is connected to an RS232EN# control input of a serial port for power management of the serial port. PPU 110 thus provides important advantages of single-chip control of multiple power voltages and further combined with a suspend function. Display chip 114 is suitably a C&T 65530 or Cirrus Logic GD6545 among commercially available examples. Display chip 114 when activated, sends a control voltage VEE_ON to power supply 172 to cause the supply to provide contrast voltage VEE to LCD 190. The level of VEE is controlled by VEE ADJ block in response to knob 34 of FIG. 1. Display chip 114 is suitably configured as a PCI-compliant chip with internal PCI interface circuitry and configuration registers so chat it returns a device select signal DEVSEL# to PPU 110 when active. Display chip 114 is connected to directly send video information to the LCD 190, as well as to send a BL-ON control signal to activate a Back Light Inverter P.S. power supply to invert a low voltage VDC from supply 172 to hundreds of volts or otherwise as suitable for a fluorescent back light in LCD 190 and supply the result to LCD 190 responsive tc back light adjust BLADJ PWM signal from PPU 110. Graphics and text outputs are also provided by display chip 114 in video form to display circuitry 192, 194 and 196 of FIG. 7. MPU 102 is connected to power management circuit section 920A at pins SMI#, MASKCLK#, 32KHZCLK and SUSPEND#. The latter SUSPEND# line not only connects to MPU 102 and PPU 110 but also connects to and controls a SUSPEND# pin of a power control chip U11 (see FIG. 52 detail) associated with PCU 112 and a 5V_ON pin (also called low-active shutdown SHDN# in FIG. 52) of power supply 172. PCU 112 supplies card system management interrupt CRDSMI, as well as three routable interrupt request lines for card A and card B (CRDAIORQ, CRDBIORQ) and card service request CRDSRVRQ. Circuitry 124 provides general purpose SMI to the GPSMI pin of PPU 110. From a system partitioning point of view, the power management logic has circuit 920 in PPU 110 as a first integrated circuit on a first chip. MPU 102 has a second power management integrated circuit having the control input SUSPEND# and this second power management integrated circuit is thus provided on MPU 102 as another chip coupled to the first integrated circuit PPU 110. Indeed, The power management circuitry is distributed not only in PPU 110 as the main center for this function, but also PCU 112 and display controller 114 as well as MPU 102. This embodiment thus provides power management improvements locally in each chip and also globally in the system into which the chips are interconnected. High speed circuits for clock control (see e.g. FIG. 36) are concentrated in MPU 102 and advantageously partitioned from the lower speed circuits for clock control of PPU 110 (see e.g. MASKCLK and 32KHz. of FIG. 24), thereby also minimizing radio frequency interference (RFI) and timing problems. This embodiment illustrates an example of an improved system arrangement that has a microcomputer integrated circuit (e.g., 102) having a first power management circuit, an interface integrated circuit (e.g. 112) adapted for coupling a memory card to said microcomputer integrated circuit (102) and having a second power management circuit, a peripheral processor integrated circuit (e.g. 110) having a third power management circuit coupled to each of the first power management circuitry of said microcomputer integrated circuit and the second power management circuit of the interface integrated circuit, the third power management circuit controlling the first and second power management circuits via control lines coupled to each of the first power management circuitry of said microcomputer integrated circuit and the second power management circuit of the display controller integrated circuit. Each of the first, second and third power management circuits comprises transistors and said third power management circuit has at least four times as many transistors as each of the first and second power management circuits. Also provided is a display controller integrated circuit having a fourth power management circuit coupled to the third power management circuit in the peripheral processor integrated circuit. A card system management interrupt CRDSMI output from PCU 112 is connected to a corresponding CRDSMI input of PPU 110. PCU 112 I/O request outputs for Card A (CRDAIORQ), Card B (CRDBIORQ), and CRDSRVRQ are also connected to corresponding inputs of PPU 110. A general purpose system management line GPSMI is provided between GPSMI pins of FPGA 124 and PPU 110 for FPGA signaling to the PPU. Display controller chip VGA 114 is enabled by a VEE_ON control signal from power supply 172. A further control signal Back Light On BL-ON# is low-active and controls the on/off state of the back light of LCD 190 (Liquid Crystal Display). Backlight systems for a monochrome type of LCD display can contribute 2-3 watts to system 100 power consumption without power management. Thus display power management is important. When user I/O interfaces such as keyboard, mouse and display are idle, as determined by activity timers, the display can be dimmed or shut off. The keystroke that causes power management mode exit (to bring the display back on or full on) is suitably ignored for user convenience. VGA LCD controllers have an ouput signal VEE enable used to enable or disable LCD VEE power and used to generate contrast. A first method of providing this convenience, for example, comprises a first step of routing a screen blank status signal (e.g. a VEE enable signal) to the keyboard controller/scanner KBC 118. Then in a second step the KBC BIOS is programmed to ignore or prevent system response to any keystrokes when VEE enable is inactive. A second alternative method of providing this convenience comprises a first step of routing the screen blank status signal (e.g. a VEE enable signal) to a system management interrupt (SMI) input such as GPSMI on PPU 110. A second step generates the SMI when the display is disabled. In a third step, system management software responds to the SMI and sends a command to the KBC 118 to ignore the next keystroke, with the system free of any independent data path for VEE enable to KBC 118, and compatible with use of KBC 118 for additional power management functions. The SMI is further advantageously used by power management BIOS in determining system activity. Circuitry 1900 is shown as a block in FIG. 20 and detailed in FIG. 21 for control buttons 28 and 32 of FIG. 1 as well as interconnections between the power supply 172 and PPU 110. In FIG. 21 power supply 172 is coupled to the PMU 920 of PPU 110 in part of electronic system 100 of FIGS. 5-7. First and second power supply connectors or sections 1902 and 1904 are electrically coupled to power management logic circuit 920 to respectively energize first logic section 920A connected to said first power supply connector 1902 and second logic section 920B connected to second power supply connector 1904. In this way, PMU second logic section 920B operation is independent of the first PMU logic section 920A such as when power is available at said second power supply connector 1904 and unavailable at said first power supply connector 1902. This condition happens when control signal VCCON is cleared by section 920B, and VCCON causes power supply 172 to turn power voltage VCC on or off. Power management logic circuit 920 has a power input VCC for section 920A and another power input RTCPWR for section 920B. A common supply rail is provided for ground connection. PPU 110 has control inputs PWRGD5 (to section 920A) and PWRGD3 (to section 920B) respectively connected to power supply 172. Active PWRGD5 and PWRGD3 indicate available 5 volt and 3 volt power respectively from the supply 172. Further PPU 110 pins for RTC section 920B provide a battery low warning input BATLOW from any appropriate battery sensor, an ON Button 28 input ONBTN, and a Suspend/Resume button 32 input SRBTN. In FIG. 21 a resistor 1912 is connected between power input RTCPWR and control input RTCRCLR, and a capacitor 1914 is connected between control input RTCRCLR and ground GND, thus providing a power-on reset function for RTC section 920B which has a state machine 2030 of FIG. 22 operative as an internal logic circuit adapted to go to a particular state in response to a voltage on the RTCRCLR control input indicative of a lack or failure of power. The FIG. 21 power supply 172 which has a 3 volt battery and a 5 volt supply circuit also operable from residential or office wall socket, is connected to first power supply connector 1902. Power supply 172 provides respective system-wide reset signals designated PWRGD3 and PWRGD5 for all devices as may be desired to utilize such reset signals on the 3.3 volt and 5 volt power planes of FIG. 62 circuit board 302 respectively. A second power supply such as a temporary power cell (e.g., coin cell) 1930 is connected to a further power supply connector 1932. A power-channeling circuit 1936 is connected to both supply connectors 1922 and 1932 and to power input RTCPWR of PPU 110. Power-channeling circuit 1936 has a pair of diodes 1942 and 1944 connected together at their cathodes and therefrom to power input RTCPWR. Diodes 1942 and 1944 also have their anodes connected separately to connector 1904 for supply 172 and to connector 1932 via a drain-limiting resistor 1946 for coin cell 1930. Power management logic circuit section 920B has logic (in circuitry 2010 of FIG. 22 for system on/off responsive to a first control input ONBTN, and ON/OFF switch 28 of FIG. 21 coupled to input ONBTN via a contact bounce suppressor having a parallel combination of a resistor 1954 and capacitor 1956. Further logic in circuitry 2010 of FIG. 22 provides for suspension and resumption of operation responsive to a control input SRBTN, and SUSPEND/RESUME switch 32 of FIG. 21 is coupled to input SRBTN via its own contact bounce suppressor having a parallel combination of a resistor 1964 and capacitor 1966. The outputs of Button Response circuit 2010 are ON Button Trigger pulse OBTNTGR and Suspend/Resume Button Trigger pulse SRBTNTGR. A MOSFET transistor 1970 is connected between both switches 28 and 32 and the ground supply rail. The transistor 1970 is controlled by a voltage at a battery-dead terminal BATDEAD# (see connector 1904) to disconnect both switches 28 and 32 from the ground supply rail when the voltage at the battery-dead terminal is indicative of a battery-dead condition. Further in connection with BATDEAD# is a diode 1972 connected between BATDEAD# terminal of supply 172 and pin PWRGD3 of PMU 920, to inactivate PWRGD3 at PMU 920 when the battery is dead (BATDEAD# low). A resistor 1974 is provided between the PWRGD3 terminal of PMU 920 and PWRGD3 terminal of supply 172, advantageously limiting current from PWRGD3 of supply 172 in case it is high when BATDEAD# is low and overriding the PWRGD3 supply 172 signal. A leakage control circuit 1975 is implemented on-chip in PMU 920, to eliminate a leakage current which flows through the ONBTN AND SRBTN button inputs of the chip 110. Nominally ten microampere (10 uA) pull-up p-channel FET transistors 1976-ON and 1976-SR are respectively connected between power conductor RTCPWR (also called VCC_RTC) and the on button input pin ONBTN or the SR button input pin SRBTN. Nominally one hundred microampere (100 uA) pull-down n-channel FET transistors 1978-ON and 1978-SR are respectively connected between the ground or common power conductor and the on button input pin ONBTN or the SR button input pin SRBTN. A NAND gate 1979 has its output connected connected to the gates of both transistors 1978-ON and 1978-SR. NAND gate 1979 further has its output connected to the input of an inverter 1977. The output of inverter 1977 is connected to the gates of both pull-up transistors 1976-ON and 1976-SR. NAND gate 1979 is fed by a programmable input bit INBLRES and qualified by inputs for signal SUSPEND and low battery BATLOW. NAND GATE 1979 determines whether the pull-ups 1986-ON and 1986- S R should be disabled through inverter 1977 connected between the output of NAND gate 1979 and the gates of those pull-ups. If the INBLRES bit is reset to zero (0), the pull-ups are enabled; if it is set to one (1), then the pull-ups are disabled when the system is in either the 5V SUSPEND or 0V-SUSPEND states of below-described state machine 2030, provided the BATLOW input is active. The output of NAND gate 1979 is also connected to the gates of both of the pull-downs 1988-ON and 1988-SR. In this way the inputs ONBTN and SRBTN to a Button Response Circuit 2010 of FIG. 22 are free of leakage, thereby increasing battery life of system 100. Circuitry 1980 of FIG. 21 advantageously recognizes that even when the lid of notebook 6 of FIG. 1 is down, thus pressing suspend button 32, the notebook 6 should be on and/or resumed if it is inserted into docking station 7 and docking station power is on. In FIG. 21, notebook 6 upon insertion makes connection via connector 45 of FIG. 3 or connector 89 of FIG. 4, as the case may be. A grounded pin GND of this connector 45 mates to a notebook pin that is otherwise pulled up by a resistor 1981 connected to notebook VCC (indicated as a top-hat on the resistor 1981). Insertion causes pin GND to pull down the notebook pin and thus the emitter of an NPN bipolar transistor 1982, as well as an input of an inverter 1982 described later hereinbelow. Also upon insertion, a VCC pin of connector 45 of docking station 7 7 places voltage across a pull-down resistor 1984 in notebook 6. This voltage causes current flow through a resistor 1985 to the base of transistor 1982, turning transistor 1982 on, and forcing the bases of a pair of PNP bipolar transistors 1986 and 1990-SR and their base pullup resistor 1987 low via the collector of transistor 1982. The collector of transistor 1982 is suitably made available for sensing at an I/O port of the system. The emitters of transistors 1986 and 1990-SR are connected high in notebook 6, and with bases low, transistors 1986 and 1990-SR turn on, and their collectors go high. An NPN transistor 1990-ON has its emitter grounded and its base commonly connected to and ordinarily pulled down by a resistor 1991. When transistor 1986 collector goes high, however, current flows therefrom to the base of transistor 1990-ON via a resistor 1992, turning on transistor 1990-ON whereupon its collector goes low. A pair of resistors 1995 and 1996 connect the collectors of transistor 1990-ON and 1990-SR to the respective ONBTN and SRBTN inputs of PMU 920B. With transistor 1990-SR conductive, the SRBTN input is forced high regardless of the state of switch 32, resuming the notebook 6. In case the notebook 6 had button 28 turned OFF (switch open), the conductive transistor 1990-ON pulls PMU input ONBTN low and turns on the notebook 6. Advantageously, when the notebook 6 is away from docking station 7, transistors 1990-ON and 1990-SR are nonconductive, and their independent connections to inputs ONBTN and SRBTN prevent any cross-coupling or unintended operation at either of these inputs. Circuitry 1980 is also suitably implemented in CMOS transistors and located on-chip in PMU section 920B of PPU 110. Circuitry 1980 is made responsive in such embodiment to an input pin DOCK connecting to VCC of docking station 7 upon insertion of notebook 6. Upon power-up in notebook 6 caused as described above by insertion into docking station 7, inverter 1983 is enabled by a voltage from FPGA chip 124 (FIG. 6) detecting a polling request signal from software. Inverter 1983 output goes high on XBUS XD due to its input low. The output high is polled by the software so that system 100 detects valid insertion of notebook 6 into docking station 7 whereupon software releases the inverter 1983 enable. In FIG. 22 power management section 920B in PPU 110 has a button response circuit 2010, a VCCON generator 2020, a state machine 2030 and register block 2040. The button response circuit debounces the button inputs ONBTN and SRBTN producing respective active-high, predetermined duration, button trigger pulses OBTNTGR and SRBTNTGR in response to the first low-going transition for the respective button input and ignoring any other input activity for that button for a predetermined duration which is longer than the trigger pulse. VCCON generator 2020 and state machine 2030 are described in FIG. 23. Further in FIG. 22, register block 2040 includes five register bytes at locations 0A0h-0A4h which retain important data for the power management unit 920. These registers are described in a tabulation of PMU registers elsewhere herein, and include 3 bytes at 0A0-0A2h for 24-bit register PMU-Control, an open byte at 0A3h for register expansion, as well as a byte at 0A4h for 8-bit register Mask-Resume. Data is read or written to/from bus 904 on lines WRDATAx (x=register identifying number 0-4) to the register x. A register address decode block 2045 decodes addresses on an address portion ADR of bus 904, and when an address 0A0-4 of a register x in block 2040 is detected, a Write-Register clock input WREGAxh is activated for the appropriate register byte indicated generally by spaces 7-0 in block 2040 of FIG. 22. In FIG. 21 a state transition diagram of state machine 2030 has six states READY (0,0) state 0, STANDBY (0,1) state 1, TEMPORARY state 2, 5V SUSPEND (1,0) state 3, 0-V SUSPEND (1,0) state 4, and OFF (1,1) state 5. The circuitry of state machine 2030 is sequential logic established in random logic, or in a PLA (programmable logic array), in a control ROM or any other form suitable for the application at hand. The state machine 2030 remains in any one current state reached by it until a transition signal initiates a transition from the current state to another state predetermined by the identity of the alphabetically letter designated transition signal as defined in the Transition State Table herein. Transitions occur from any one of the six states to another of them in response to transition signals associated with the illustrated transition arrows A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R. Also, the state transition diagram represents steps in a preferred method of operation in system 100, PPU 110, PMU 920 and RTC 920B. STANDBY mode activates pulse width modulation of the MPU 102 clock as in FIG. 27. Transitions into and out of STANDBY state or mode involve clock control considerations due to a phase lock loop PLL internal to MPU 102 as described in connection with FIGS. 33, 34 and 36. If the CPU clock is fully stopped, the DOS timer tick (IRQ0 of FIG. 43) is not executed, so the DOS clock is updated based on the battery powered RTC 918 of PPU 110, when the Standby mode is exited. 5V SUSPEND Mode keeps most motherboard 302 (FIG. 8) logic powered but in a static low power state, and transition out of this mode quickly resumes the user application that was executing beforehand. This mode is preferable to the OFF state except when the battery pack simply goes dead or is removed. System power consumption in the milliwatt range or less can be achieved in 5V Suspend mode, and this consumption is comparable to the power loss associated with the self discharge current in NiCad and NiH cells. Clock control for 5V Suspend turns oscillators and PLL off, as contrasted with Standby Mode which keeps them going and gates clocks out. In the preferred embodiment, the PCI and CPU clocks make the clock transitions off and back on in a glitch free manner with minimum pulse widths maintained. Clocks to devices that are reset when Resuming need not be restarted cleanly. Power supply surge currents during 5V Suspend/Resume transitions are reduced or eliminated by keeping signals driven to VCC rails during these transitions. Also, the power supply 172 is suitably designed to accommodate surges with control circuitry that operates in a constant frequency, pulse width modulated (pwm) mode for larger output currents, and operate in a hysteretic control mode for lower output currents. Zero volt suspend (0V SUSPEND) stores the state of the computer to disk before powering the system off. In this way, the state of the computer can be restored as in 5V Suspend mode, with the main difference being a longer amount of time to resume from OV Suspend due to HDD spin up time and saving the state of trackball/mouse 144. A first method of trackball/mouse state save comprises the step of adding a custom command to the trackball scanner 118, then executing the command to read the state of the trackball/mouse, and saving the state of the trackball/mouse thus read. A second different method of trackball/mouse state save comprises the step of adding custom code to a keyboard controller to store host CPU commands related to the trackball state as these commands are sent to the trackball. Upon entry of the 0V Suspend state, a next step executes these commands read the state of the trackball/mouse, and an additional step saves the state of the trackball/mouse thus read. Swapping battery packs without losing 5V Suspend power is successfully accomplished by an on-board-302 VCR capacitor and/or rechargeable lithium cell. A one-farad VCR capacitor can provide 5V Suspend power for about half a minute. Rechargeable lithium coin cells such as coin cell 1930 of FIG. 21, can provide one or more hours of 5V Suspend power. Additional circuitry is suitably provided to charge the coin cell in FIG. 21. An optional diode 1945 or a FET transistor circuit similarly connected in place of diode 1945 in FIG. 21 advantageously charges the coin cell 1930 when it is low on charge. Docking station VCC is supplied to a CHARGE input of power supply 172 for battery charging when the notebook 6 is inserted. In FIG. 23, some output signals from the state machine 2030 are developed by combinational logic using the states (assumed high active for illustration) as inputs. For example, a signal HISPD indicative of high speed operation is active at the output of an OR-gate 2102 when state machine 2030 is in either READY or TEMPORARY state. Another signal RS is active at the output of an OR-gate 2104 when state machine 2030 is in either the STANDBY or the TEMPORARY state. A SUSPEND signal output pin 2110 from PPU 110 becomes active at the output of inverter fed by an OR-gate 2112 when state machine 2030 is in either the 3-V SUSPEND or the 0-V SUSPEND state. A NOR gate 2114 provides a complementary signal SUSPENDZ in response to SUSPEND as one input and the OFF signal as another input. A low-active control signal CLRVCCON# (Clear VCC ON) is supplied by a NOR-gate 2122 from inputs 0-V SUSPEND or OFF. Among its other advantageous features, power management logic 920 thus has a state machine circuit 2030 having a plurality of states (FIG. 23) in addition to an OFF state (OFF representing that the system is to be turned off). The state machine circuit 2030 is adapted to respond to presence of power from power supply connector or section 1904 (FIG. 21) when power is absent from a first power supply connector 1902, to transition from at least one of the plurality of states in FIG. 21 to the OFF state. STANDBY Mode involves slowing, masking or stopping the CPU clock, and other clocks are suitably controlled as well. The MPU 102 may be the second largest power consumer in a backlit portable PC system 100 and thus is a target for power management. In FIG. 23 the VCCON generator 2022 of FIG. 20 is detailed further, showing the development of the signal at output pin VCCON of PPU 110. Transition logic 2140 is combinational logic that develops the clock signals A-R for latches that define the six states of state machine 2030 according to the Transition States Table. Also, part of this logic 2140 develops a signal WAKEUPRTC (same as causes transition R of the Table) for VCCON generator 2020. A MASK_RESUME register tabulated elsewhere herein allows selected event-sources such as CN-button, S/R button, modem ring, alarm, etc., to be masked or selected to resume the system in Transition "O" from 5V-SUSPEND to READY as tabulated. In the VCCON generator 2020, the control pin 2128 input RTCRCLR# is fed to a NAND gate 2154 as well as a NAND gate 2156. The output of gates 2154 and 2156 are connected to respective inputs of a NAND gate 2160 which drives the VCCON output pin. Control signal WAKEUPRTC is fed to another input of NAND gate 2154 and is inverted by an inverter 2166 which feeds another input of NAND gate 2156. Signal CLRVCCON# is connected from the output of NOR gate 2122 to a third input of NAND gate 2156. In this way, when RTCRCLR# is low, it forces the outputs of both NAND gates 2154 and 2156 high, forcing the VCCON output of NAND gate 2160 low, clearing VCCON. If RTCRCLR# is high, however, it qualifies both NAND gates 2154 and 2156. If WAKEUPRTC is high, then NAND gate 2154 output goes low, forcing the VCCON output of NAND gate 2160 high, thereby turning on VCCON as part of a wake-up function. If RTCRLCR# is high, and WAKEUPRTC is low, then both NAND gates 2154 and 2156 are qualified as before, but the low WAKEUPRTC forces the output of NAND gate 2154 high, qualifying NAND gate 2160, and inverter 2166 feeds a high qualifying input to NAND gate 2156. Then CLRVCCON# (active low) controls output VCCON (because both NAND gate 2156 and NAND gate 2160 are otherwise qualified), and, for example, a low or high signal CLRVCCON# forces output VCCON low or high respectively. In FIG. 24 PMU portion 920A has a clock divider circuit 2310, an oscillator control circuit 2320, a backlight PWM generator 2330, a mask clock generator 2340, a timer circuit 2350, status counters circuit 2360, system management interrupt circuit 2370, a peripheral power control circuit 2380, a Resume 5V circuit 2385, and a Reset generator 2390. All the circuits in this PMU portion run under power from the power supply in this embodiment, and not from a battery like RTC 920B, so that RTC 920B can disable all these circuits in section 920A. Clock divider circuit 2310 in PPU 110 is realized by a multistage counter 2312 that has a 32 KHz, clock input from MPU 102 of FIG. 1. Counter 2312 is resettable when power is uncertain, by an externally supplied control signal PWRGD5 to turn the system off upon the completion of at least one clock cycle of the clock circuit. The counter 2312 has 14 stages and provides successive divide-by-two clocks at 16, 8, 4, 2, and 1 KHz, and 512, 256, 128, 64, 32, 16, 8, 4, and 2 Hertz. Clock divider circuit 2310 further has a divide-by-14 circuit 2314 clocked by 32 KHz. input to produce an output clock with a period of 430 microseconds (a little faster than 2 KHz.). Still another circuit 2316 divides the counter 2312 four (4) Hertz output by fifteen (15) to produce a clock with a period of 3.75 seconds. A clock substitution circuit 2318 substitutes 32 KHz. for each of the 512 Hz. and 2 Hertz outputs, and 4 KHz. for the 3.75 sec. clock output, in response to the PWRGD5 signal and a test input. Oscillator control circuit 2320 is responsive to the 512 Hertz clock, PWRGD5 and SUSPENDZ signals to sense the clock oscillator state as OSCILLATOR STABLE, OSCILLATOR OFF, AND OSC14M STABLE. Circuit 2320 senses a number of successive cycles to determine stability. PWM generator 2330 has a 4-bit or other multibit software programmable control register 2332 to produce a backlight adjust control signal at a BLADJ output pin of PPU 110. Register 2332 variously qualifies clocked-AND-gates and clocked OR-gates in a logic circuit 2334 and thereby controls a combination of clock pulses from 1 KHz., and 512, 256 and 128 Hertz clock outputs of clock divider circuit 2310 to establish the duty cycle of the BLADJ signal in correspondence to the binary value represented by the bits in register 2332. For example, each clock has a 50% duty cycle. ANDing two of them together reduces the duty cycle to 25%. ORing two of them increases the duty cycle to 75%. The results of the AND and OR can be still further logically combined with other AND and OR operations with the other clocks to produce a continuous range of duty cycles. If all the bits are ones, then BLADJ has 100% duty cycle for full-on back lighting of system 100 by the BACK LIGHT of FIG. 2. Mask Clock generator 2340 in PPU 110 advantageously provides a pin output MSKCLK# variable duty cycle low frequency control signal to periodically turn on and off the high speed clock in MPU 102, as described in more detail by reference to FIG. 25. Timers block 2350 produces timer outputs for system management interrupt block 2370 of FIGS. 23 and 26 and for peripheral power circuit 2380. Timers block 2350 is described in more detail in connection with FIG. 24. Status counters block 2360 provide software readable event history statistical information accessible from bus 904 and useful in active power management software such as in FIG. 45. Status counters block 2360 includes status information for I/O such as serial port COM1, parallel port LPT1, mouse MSINT, keyboard KBINT, bus 104 interrupt (e.g. PCI-INTA), drive trigger signal DRVTGR, X-drive signal XDRV, and display (e.g. VGA). For example, a 4-bit KBCS counter 2362 (or a counter of any of the above-listed event signals) counts KBCS event pulses and produces an output status register value STKBCS (which counts the number of events of that type since the last poll by software) which is software accessible (such as by active power management software or by BIOS) to facilitate program monitoring and control of the system based on the counter information developed in and concatenated from the status counters block 2360. These counters saturate and do not roll over and instead are reset when desired. A LAN event counter is weighted differently from a HDD event count by active power management software, for example. System Management block 2370 is described in more detail in connection with FIG. 28. It has SMI period register control bits SMIPRD, and timer inputs from timers block 2350. Also, another SMI input receives a power management unit reset PMURST signal that also resets some PMU 920 circuitry on return from 5V SUSPEND. Peripheral power block 2380 produces PPU 110 output signals for 1) hard disk power IDEPWR, 2) floppy disk power FDDPWR, 3) serial interface unit power SIUPWR and 4) programmable chip select power PCSPWR. The foregoing numbers 1-4 representative of IDE, FDD, SIU and PCS are indicated by "x" in the following description. Peripheral power block 2380 has four AND gates 2382.x producing outputs xPWR to output pins. All four of AND gates 2382.x are qualified at a first input by the enable power management unit ENPMU signal. Each AND gate 2382.x has a second input connected to an output of a corresponding NAND gate 2384.x, and a third input connected an output of a corresponding OR-gate 2386.x. Each NAND gate 2384.x has a first input connected to a respective enable control signal SWCNTLx corresponding to bits 7, 5, 3 and 1 of the SW_PWR_CNTL register and a second input connected to a respective high active power signal SWxPWR corresponding to bits 6,4,2 and 0 of the SW_PWR_CNTL register tabulated elsewhere herein. NAND 2384.x inverts SWxPWR to produce low-active output for FIG. 20 power on in block 170, in advantageous software-controlled power management. Each OR-gate 2386.x has a first input connected to the respective software control signal SWCNTLx as above and a second input connected to a respective timer time-out hardware control signal xTO, in advantageous hardware-type passive power management. When software control enable SWCNTLx is low (software control disabled, hardware control enabled), and xTO goes high on hardware timer timeout for that peripheral x, then power is cut off to the timed out peripheral x via AND gate 2382.x suppling inactive-high to a line for that peripheral in block 170 of FIG. 20. Resume 5V circuit 2385 provides a wakeup from 5V-SUSPEND state 3 of the state machine 2030 of FIG. 23. A register 2386 has the software-readable eight top 16-23 bits of the PMU_CNTRL register as described in the table for that register. Notice that the function of the Resume 5V circuit 2385 is closely associated with the state machine 2030 in the 3 volt well 920B but the location of the Resume 5V circuit 2385 is in the 5 volt well in circuit 920A. This physical layout embodiment keeps gate count low in the 3 volt well 920B and keeps power consumption low when only the 3 volt well 920B is powered. Reset Generator 2390 supplies outputs to PPU 110 pins IDERST for hard disk reset, FDDRST floppy disk reset, and XDRST for peripherals on the XD bus. Internal resets PMURST for the power management circuitry 920 and a bus 104 reset BUSRSTOUT (e.g. BUS=PCI) are also provided. In FIG. 25 Timers block 2350 in PMU section 920A of FIG. 23 has eight timer counters, each fed four-bit codes from eight (8) corresponding four-bit sections of a software-accessible 32 bit register PMU_TIMERS connected to bus 904. The sections and corresponding timers for this register PMU_TIMERS are tabulated under its name elsewhere in. Also tabulated are a translation of the four-bit codes into time-out values. A 0000 code disables each timer. The timer timeout values are 0-15 minutes with minutes coded to binary, except that the Standby Timer STDBY is nonlinearly coded up to 15 minutes as shown for bits 31-28, and that the Temporary Timer TEMP is nonlinearly coded in tens of microseconds and then in milliseconds up to 15.36 milliseconds. The VGA timer is linearly coded up to 14 minutes and then "1111" equals 8 seconds. Further in FIG. 25, timers PCS, SIU, VGA, FDD, IDE, and SUSP are all eight-bit binary counters, each with one time-out digital output lines fed by a 4-bit comparator (indicated by XOR exclusive OR symbol) that compares the four MSBs (most significant bits) of each counter with the 4-bit code supplied from register PMU_TIMERS. Each of these six just-mentioned counters have a clock input connected to the 3.75 second period clock from block 2316 of FIG. 25. The timer STDBY has its clock input connected to the 2 Hertz output from block 2312 of FIG. 23. The short-time timer TEMP is clocked directly by 32 KHz. clock. Timers TEMP and STDBY have timer decode circuitry 2410 and 2420 respectively connected to the counters 2412 and 2422 in each timer. The timer decode circuitry 2410 and 2420 each provide 16 output lines to OR-gates 2414 and 2424. Only one of the 16 output lines from each timer TEMP and STDBY is high at any time, depending on the results of the decode. The eight timer counters each have a reset input which is responsive to a respective block of combinational logic 2430 having an OR gate 2432.1 - .8. A first input of each OR gate 2432.1-.8 is connected to the output of a common AND gate 2440. The latter gate 2440 provides an active output when PMU reset signal PMURST is active and a register write signal WREGBCH is active. (BC hex is an address.) A MASK_SIU_VGA register is tabulated with the rest of the timer registers, and provides signals (designated with the prefix MASK ahead of event names COM1, LPT1, KBMS, VGA) which mask system events when they are not intended to be monitored by the timer SIU or VGA associated with the combinational logic 2430 fed by a signal line for that event. The reset logic for the timers is illustrated in FIG. 24. This reset logic confers advantages including important system flexibility and power management configuration. For instance, keyboard activity via KBMSTGR can be used or not (depending on mask bit MASKPKBMS), for resetting the VGA display timer in FIG. 25. Analogous statements are evident for each of the various triggers _TGR and masks in the context of the circuits to the timers of FIG. 25. In FIG. 25, the reset logic of the SUSP, TEMP and STDBY timers is described further. A suspend reset event SUSPTGR is implemented in combinational logic MASK LOGIC by OR-ing the outputs of fifteen AND gates. The fifteen AND gates respectively AND together each of 15 system event signals with its corresponding mask bit in the set of mask bits 0-14 (event prefixed by SUSP for mask) in register MASK_SYSTEM as described in its tabulation. A standby reset event STDBYTGR is implemented in combinational logic by OR-ing the outputs of another fourteen AND gates in MASK LOGIC. The fourteen AND gates respectively AND together each of 14 system event signals with its corresponding mask bit in the set of mask bits 16-29 (event prefixed by STDBY for mask) in register MASK_SYSTEM as described in the tabulation for that register. Refer to FIG. 15 for HLDA and FIG. 23 for state or mode signals to timers of FIG. 25. In FIG. 26, a description of the STDBY nonlinear timer is given in detail. The description of the TEMP nonlinear timer in one embodiment is the same, and therefore omitted, except that the input clock is as shown in FIG. 25, and the connection to PMU_TIMERS register is analogous. In another embodiment the TEMP timer is different as is shown in the upper part of FIG. 26 and described. In FIG. 26, STDBY timer has a counter 2422 clocked by 2Hz. clock and reset by logic of FIG. 25. The 4 bit nibble STDBY in register PMU_TIMERS is fed to the 4-bit input of a 4-to-16 binary decoder 2455. Sixteen lines from the 16-bit output of decoder 2455 connect to 16 first inputs of 16 NAND gates 2457.1, 2457.2,...2457.16 respectively. Counter 2422 produces a multi-bit value which is fed to a decode circuit 2460 which has as many outputs (e.g. 16) as there are NAND gates 2457.n. The decode 2460 has combinational logic which is arranged to produce an output high on only one of the sixteen lines at a time, wherein each line connects to one of 16 respective second inputs of NAND gates 2457.n, and corresponds to a table row in the tabulation for bits 31-28 (STDBYTMR3-0) in the tabulation for the PMU_TIMERS register elsewhere herein. A high on such line corresponds to the occurrence of a counter 2422 value representing the amount of time tabulated in one of the 16 table rows. These times are nonlinear as a function of table row number, in general, and the circuitry of FIG. 26 efficiently performs a nonlinear timer function (with linear as a special case). This nonlinear function can be hardwired into the decoder 2460. Also, an optional programming register 2465 accessible from bus 904 is in a second embodiment provided to drive decoder 2460 in programmable form to implement any tabulation desired. Sixteen outputs of the NAND gates 2457.n are supplied to 16 inputs of a single NAND gate 2470 (analogous to OR-gate 2424) to provide the STDBYTO output. When STDBYTO goes active it clocks a latch 2472 which disables an AND-gate 2474 from passing clock to counter 2422, thereby freezing the counter 2422 value. The counter 2422 can be restarted by a RESET signal on a line connected to the reset inputs of Latch 2472 and counter 2422. In FIG. 26, TEMP timer has a nine-bit counter 2412 clocked by 32KHz. clock and reset by its own logic of FIG. 25. The 4 bit nibble TEMP in register PMU_TIMERS is fed to the 4-bit input of a 4-to-9 mapper circuit 2484 such as a ROM, PAL or combinational logic. The nine bit outputs of counter 2412 and mapper 2484 connect to first and second 9-bit inputs of a comparator 2486 to produce an output HWTO indicative of equality or not. Note that TEMP points to a table row in the tabulation for bits 23-20 (TEMPTMR3-0) in the tabulation for the PMU_TIMERS register elsewhere herein, and the 9-bit mapper 2484 output corresponds to the amount of time tabulated in one of the 16 table rows. These times are nonlinear as a function of table row number, in general, and the circuitry of FIG. 26 efficiently performs a nonlinear timer function (with linear as a special case). This nonlinear function can be hardwired into the mapper 2484. Comparator 2486 detects or responds to an occurrence of a counter 2412 value representing the mapper value to which the TEMP input thereto points. When any one of hardware timeout HWTO, or a software time out line SWTO or a WSO1 control line go active at the inputs of an OR-gate 2488, the output of OR-gate 2488 supplies a high to the D input of a latch 2490 clocked at 32 KHz, thereby providing a Q output TEMPTO for the timer block 2480. When TEMPTO goes active it feeds back to a gate 2492, which prevents 32KHz clock from reaching counter 2412, thereby freezing the counter 2412 value. The counter 2412 can be restarted by a reset signal on a line RST# connected to the low-active reset R inputs of Latch 2490 and counter 2412. In this way a variety of nonlinear timer embodiments provide speed, programmability, and die area advantages for power management units, timers and integrated circuits generally. In FIG. 27, the Mask Clock generator 2340 in PMU section 920A of PPU 110 has a software programmable register MASK_CPUCLK (also called TONTOFF) 2510 programmable from internal bus 904 when clocked by signal RREGD0H (decode of D0 hexadecimal register address). A clock signal (e.g., 2 KHz or the 430 microsecond clock) from clock divider 2310 is fed to a 7 bit counter 2520 which counts clock cycles from 0 to 127 and repeats continually. A system reset resets this counter 2520. A comparator 2530 outputs a logic one or zero signal AGTB depending on whether the count in counter 2520 is greater or less than the count in register 2510. Signal AGTB is connected to gating logic 2535. When logic 2535 is qualified by presence of the STANDBY mode, and logic signals trigger input TGRIN#, and mask clock enable MC#, then AGTB passes to an output pin MSKCLK# of PPU 110. As shown in the waveform diagram in FIG. 27, MSKCLK# has a repetition rate of about 18 Hertz, with a period of 55 milliseconds, when the 430 microsecond clock is counted. 7 bit counter 2520 divides rate by 128, so 430 microsecond period is multiplied by 128 to yield about 55 milliseconds. This low frequency signal is coupled from PPU 110 to MPU 102 as shown in FIGS. 5, 6, and 27. In MPU 102, an AND circuit 2540 gates the nominal 50 MHz. MPU 102 clock to the operative parts of MPU 102 in response to the advantageously variable duty cycle MSKCLK# control signal. Inside MPU 102 the waveform 2545 of the gated clock has a first interval 2550 of high speed pulses followed by another interval 2552 of no high speed clock pulses. The time intervals 2550 and 2552 are the same in both MSKCLK control signal and the gated clock wavoform 2545. The frequency of MSKCLK is advantageously low since it is coupled between chips 102 and 110 on printed wiring board 302 of FIG. 8. The gated clock circuitry advantageously occupies only a small area inside MPU 102. The low frequency of MSKCLK# modulating the very high frequency of the CPU clock does not produce significant harmonics, and advantageously avoids radio frequency interference (RFI) or other electromagnetic interference (EMI) at the system or device levels. The circuitry embodiment as described provides an illustration of an electronic device that has a register for duty cycle data (e.g. TONTOFF) and a clock circuit coupled to the register and control circuitry responsive thereto configured to repeatedly generate an output having a duty cycle responsive to the data and then a plurality of series of clock pulses, the series interspersed or followed with intervals free of, or lacking, clock pulses. Each series has a number of clock pulses and that number is responsive to the data in the register. The register and clock circuit are integrated onto one integrated circuit chip. A microprocessor (e.g. MPU 102) is connected to receive the duty cycle variable output as a modulating signal to produce the series of clock pulses to clock the microprocessor, whereby a resulting modulated clock is has a duty cycle established by the data in the register. The interval free of clock pulses also has a complementary length responsive to the data in the register. The clock circuit has a clock rate, and the series of clock pulses has the same clock rate. The microprocessor device is fabricated on a first integrated circuit, and the clock circuit and register are fabricated on a second integrated circuit chip coupled to said first integrated circuit chip. Also represented by FIG. 27 is a method of operating a computer system having a microprocessor device and a clock circuit, with a first step of storing data in a register, secondly controlling the clock circuit with the data, and thirdly thereby supplying to the microprocessor device a modulating or masking signal output having a duty cycle responsive to the data, and fourthly, modulating a higher frequency clock signal in the microprocessor device with the modulating or masking signal by interspersing a plurality of series of clock pulses with intervals lacking clock pulses. The control logic for the reset R input of the 7-bit counter 2520 in FIG. 27 provides important system control and flexibility advantages. For example, a signal shutting off LCD 190 as an SMI depends on the SMI masking in FIG. 28 and can be used to slow down the CPU clock. A three-input NAND gate 2560 feeds the reset input R of counter 2520, and a two-input OR-gate 2562 feeds the clock input of that counter 2520. A first input of NAND gate 2560 is fed by a NOR-gate 2564. NOR-gate 2564 has two inputs respectively connected to high active signals high-speed control HISPD and power management unit reset PMURST. If either of these latter signals are high, counter 2520 is reset and MASKCLK# is forced inactive high so that the CPU clock runs continually at high speed. These results are exactly what is desired if the state machine 2030 of FIG. 23 is in either the Temporary or the Ready state or if the power management function is reset. The rest of the control gates at left in FIG. 27 cooperate to provide a clock switch or choice circuit between 430 microsecond clock or a selectable periodic SMI (system management interrupt) clock rate from FIG. 28 (1KHz, 516, 256, or 128 Hz.). This periodic SMI clock PRDSMICLK is fed to a first input of an AND gate 2570, and the 430MS.CLK signal fed to a first input of another AND gate 2572. Only one of the AND gates 2572 is qualified depending on the clock selection represented by the output of an OR-gate 2574. A first input to OR-gate 2574 comes from bit 10 of the MASK_SMI Register tabulated elsewhere herein. This bit 10 is called mask periodic SMI or MSKPRDSMI and is fed to a first input of an AND gate 2576 and fed inverted to the first input of OR-gate 2574 and to a low active input of an AND gate 2578. When MSKPRDSMI is high, the 430 microsecond clock is selected, because OR-gate 2574 output is low and qualifies AND gate 2572. A TEST input to OR-gate 2574 can also be used to select either clock at will, when MSKPRDSMI is high. When MSKPRDSMI is low, OR-gate 2574 output goes high and passes PRDSMICLK through AND gate 2570 and OR-gate 2562 to clock counter 2520. NAND gates 2576 and 2578 perform a supporting and analogous function for counter 2520 reset. An RTC 918 (FIG. 11) timer tick IRQ0 occurs every 55 microseconds, and is fed delayed by 400 nanoseconds as a signal Delayed IRQ0 (DIRQO) to a second input of NAND gate 2576. A periodic SMI (PSMI) signal of FIG. 28 can wake up the system 100 every 1/8 second, 1/4 second, 1/2 second or every one (1) second depending on whether the selected SMI clock PRDSMICLK is 1KHz, 512, 256 or 128 Hz. respectively. A delayed periodic SMI signal DPSMI is fed delayed by 400 nanoseconds to a second input of a NAND gate 2578 in FIG. 27. The control signal MSKPRDSMI supplied to NAND-gate 2576 and low-active input to NAND 2578 performs the selection between the DIRQ0 and DPSMI reset signal candidates. If MSKPRDSMI is high DIRQ0 is gated through NAND gates 2576 and 2560 to supply a reset every 55 milliseconds. If MSKPRDSMI is low, DPSMI is gated through NAND gates 2578 and 2560 to supply a reset every DPSMI period of 1/8 second, 1/4 second, 1/2 second or every one (1) second depending on the selection in FIG. 28. As described above, the MASKCLK# circuit 2340 advantageously provides mask clock to support Standby mode at either timer tick rate or in coordination with System Management Interrupt rate. In FIG. 28 system management interrupt circuit 2370 in section 920A of PPU 110 has 24 data bit latches 2610 which respectively have 24 data inputs from a 24-bit mask register MASK_SMI 2620 which is software programmable bytewise at three byte addresses 0AC-0AE hex from internal bus 904, all as tabulated bitwise elsewhere herein. Data latches 2610 have their 24 Q outputs respectively connected to the 24 D inputs of a register 2614 called SOURCE_SMI. The 24 Q outputs of register 2614 are readable on internal bus 904 bytewise at three byte addresses 0A8-0AA hex also as tabulated bitwise elsewhere herein. This register 2614 is resettable by software when the information about which event triggered a system management interrupt is no longer needed. The mask register 2620 bits are set to one or zero depending on whether the circuit 2370 is to be responsive or not to a possible SOURCE_SMI tabulated source of SMI interrupt. The 24 data latches 2610 respectively have 24 clock inputs which are separately fed with 24 different trap signals from different interrupt sources. Among the possible interrupt sources are six I/O sources as tabulated for bits 21-16 in register SOURCE_SMI which supply latches 2630 and which have their outputs connected to bit latches 21-16 of the respective clock inputs of data latches 2610. A Periodic SMI circuit 2650 supplies a clock input of one of the latches 2610. Circuit 2650 has a 2 bit programmable SMI Period register 2652 which controls a clock selector 2654. Clock selector 2654 selects one of four clock signals (e.g., 1 KHz., 512, 256, 128 Hertz) depending on the two bits in register 2652 and passes the clock signal on to a clock input of a counter 2656 that supplies every 128th clock pulse. The output of counter 2656 is connected to a clock input of the latch for bit 10 in latches 2610. A NOR-gate 2634 has 24 inputs from the 24 Q outputs of data latches 2610. Thus a high from any unmasked interrupt source clocked into register 2610 can force the NOR-gate 2634 output SMITGR# low. Another NOR-gate 2638 produces low-active SMI output on the SMI# pin of the PPU 110 for MPU 102. MPU 102 acknowledges on the same SMI# line and executes a SMI routine in software according to a process which in a process step that suitably reads SOURCE_SMI register 2614 and in other process steps executes system management operations dependent on the source of the SMI which is flagged in register 2614. With reference to FIGS. 28, 29 and 30, the operations of SMI circuit 2370 are next described in further detail. According to conventional notation, any one of an over-bar, z suffix, or pound-sign (#) suffix usually indicate a low-active signal unless context clearly indicates otherwise. NOR-gate 2638 has four inputs including SMI trigger SMITGR# from NOR-gate 2634, CPU Reset signal CPURST, the SUSPEND signal, and a SMI generator control signal Q6. In this embodiment, a system management interrupt SMIOUT# high is generated when a SMITGR# low event is present, and the CPU is not reset, and there is no SUSPEND condition, and control signal Q6 is high. The output of NOR-gate 2638 is fed to the SMI# pin of PPU 110 when NOR-gate 2638 is enabled by low-active SMI output enable signal SMIOEZ due to Q4 low from a multibit shift register 2640. Control signal Q6 is generated in the operations of a multibit shift register 2640, here six bits long, having shift register sections 2640.1, .2, ..., .N where N=6 in this embodiment. All of the shift register sections are clocked by the same bus 104 clock signal PCLKIN (PCLKB of FIG. 6) to PPU 110. Shift register 2640 is connected in the top two bits (e.g. Q5 and Q6) to a respective pair of inputs of an AND-gate 2642. A third input of gate 2642 is qualified by the external power good signal PWRGD5. The output of AND-gate 2642 is connected to a reset input of each of the 24 data latches 2610. Recordkeeping register SOURCE_SMI 2614, by contrast, is reset by software independently of data latches 2610. When a particular two-bit code (e.g. Q5=1, Q6=0) appears at the top of shift register 2640, qualified AND-gate 2642 supplies an active high reset signal to all of the 24 latches 2610. In this way, the latches 2610 can advantageously sample the 24 interrupt sources repeatedly. Put another way, the shift register 2640 and latches 2610 advantageously cooperate to terminate SMIOUT and a system management interrupt SMI# within a period of time after the an interrupt source has ceased requesting or I/O trap signalling for the interrupt, unless the request reoccurs. Focusing even more specifically on shift register 2640, it is noted that the SMIOUT output of NOR-gate 2638 is fed back to the data input of the first section of shift register 2640, while the output of the top, or last, section Q6 of shift register 2640 is connected to one of the inputs of the NOR-gate 2638. Further, the output state of the next-to-last bit or section (Q5) of shift register 2640 is connected to low-active enable E inputs of Q1-Q4 shift register sections and used to freeze or enable transfers (shifts) from all of the lower sections to their respective next higher section, including to Q5 itself. A NAND-gate 2644 provides a reset signal to reset inputs R of register 2640 sections Q1-4, namely all but the top sections of shift register 2640, that is, all sections which are not decoded by reset gate 2642. The latter two sections are reset when signal PWRGD5 goes low. NAND-gate 2644 resets shift register 2640 sections Q1-4 when either PWRGD5 goes low or there is no SMI# active low at the SMI# pin of PPU 110. Let operations in circuit 2370, with reference to FIGS. 28-30 for purposes of description, begin with shift register 2640 reset with Q1-Q6 all low. SMI# is high and inactive until some event signal clocks a latch in latches 2610 that is not masked by register 2620, whereupon NOR-gate 2634 output SMITGR# goes low, and NOR-gate 2638 being otherwise qualified by lows, takes SMIOUT high, forcing SMI# low by PPU circuit 2370 drive. The SMIOUT high is fed to bit Q1 of shift register 2640, and successive bus 104 clock cycles shift the high bit Q1 through stages Q2, Q3, and Q4, into stage Q5. When Q4 goes high, SMIOEZ, which is the same as Q4, disables (three-states) inverter 2639, whereupon MPU 102 continues just-begun SMI-responsive low-drive single-line acknowledge on SMI# as shown by SMIIN# of FIG. 29. Now Q5 is high and Q6 is low, causing NAND gate 2642 to reset all of the latches 2610, and initiate a Trap Ignore Window of FIG. 29, whereupon with gate delays in gates 2634 and 2638, SMIOUT goes back low. Shift register 2640 Q1 goes low, but Q1-Q4 shifting is frozen because Q5 is high. The Q5 high is shifted into Q6, forcing SMIOUT low, but releasing the reset from AND-gate 2642 and latches 2610. When MPU 102 drive goes back high in FIG. 29, SMIIN goes low and resets shift register 2640 bits Q1-Q4 via NAND gate 2644. Q5 and Q6 go back low, completing the SMI cycle and terminating the Trap Ignore window. In this way, a die-area-efficient circuitry cooperates with MPU 102 to supply SMI interrupt signaling from maskable sources for SMI wake-ups and other system purposes. FIG. 31 is a partially schematic and partially block diagram of a system management interrupt circuitry 1620 embodiment in the PCU of FIG. 18 which is interconnected with the PPU of FIG. 11 and MPU of FIG. 9 to form a distributed power management system embodiment of FIGS. 31, 28, 33 and 34 interrelated with the computer system embodiment of FIGS. 5-7. In FIG. 31 the Card Status Change Register for socket A (CSC REG A) and the Card Status Change Register for socket B (CSC REG B), tabulated elsewhere herein, respectively have their bits 4,3,2,1,0 OR-ed by OR-gate 2672 and 2674 to produce respective signals A_CSC and B_CSC indicative of a change in card status change if any of five conditions GPICHG, CDCHG, RDYCHG, BWARN or BDEAD occur. For card SMI purposes, signal A_CSC and B_CSC are fed to respective first inputs of SMI NAND gates 2676 and 2678, and further respectively fed to first inputs of card service interrupt NAND gates 2677 and 2679. NAND gates 2676 and 2678 are respectively qualified by SMI enable bits SMIEN high in the Interrupt and General Control Register for Socket A and the same for socket B. If a SMIEN signal is high for a respective socket, a SMI is enabled for that socket. However, a SMIEN is low for socket A or B, enables the respective NAND gate 2677 or 2679 and gates the corresponding A_CSC or B_CSC signal to act as a card service interrupt. In the SMI circuitry of FIG. 31, two further NAND gates 2680 and 2682 provide card A or card B specific outputs for SMI purposes provided that 1) card ring indicate enable CRIEN is high for that card in Interrupt and General Control Register, 2) Ring Indicate to SMI enable is high for that card in the "Miscellaneous" Register for that card, and 3) ring indicate change RISTAT is high for that card in the "Miscellaneous" Register for that card. NAND gates 2676, 2678, 2680, and 2682 have their outputs respectively connected to four inputs of a NAND gate 2684. If any output goes low from NAND gate 2676, 2678, 2680, or 2682, then the output of NAND gate 2684 goes high whereupon succeeding inverter 2686 takes PCU 112 card SMI output pin CRDSMI# low. In this way, substantial circuitry and event data for SMI purposes are concentrated in the PCU 112 to economically supply just one pin output to PPU 110. For test purposes a NAND gate 2688 is also provided with inputs connected to NAND 2684 output and signal TESTZ to supply a signal SMIENZ. In the interrupt circuitry of PCU 112, an OR-gate 2690 is responsive to either the output from NAND gate 2677 or 2679 to supply an input to an exclusive-NOR (XNOR) gate 2692. A second input of XNOR gate 2692 is fed by a level mode/pulse mode control signal CSC_LM bit 1 as tabulated elsewhere herein for the Global Control Register. The CSC_LM bit causes the XNOR-gate 2692 to programmably inverts or not invert the output of OR-gate 2690 for advantageous level mode or pulse mode output selection. Similarly Global Control Register bit 3 card A interrupt request level mode AIREQLM and bit 4 card B interrupt request level mode BIREQLM program the operation of respective XNOR gates 2694 and 2696 fed with interrupt request lines from card A (A_IREQ) and card B (B_IREQ). The outputs of XNOR gates 2692, 2694, and 2696 are respectively coupled to output pins IRQ5, IRQ3 and IRQ4 which compactly send card service, and card A and B interrupt signals to PPU 110 as CRDSRVRQ, CRDAIORQ, and CRDBIORQ. In FIG. 32 a waveform diagram for MPU 102 shows a clock oscillator signal OSC (e.g., 50 MHZ) continuing until it is terminated by a STOPOSC control signal going from low to high at a transition 2702. Subsequently, an opposite transition startct occurs in the STOPOSC control signal, whereupon the 50 MHz. oscillator in MPU 102 is enabled and begins a number of startup cycles 2704 which are to be prevented from clocking the CPU 702. Finally, reliable clock cycles 2706 are available. A signal hresume is taken low at transition 2712 coincident with STOPOSC going high at 2702. However, signal hresume is made to go high at transition 2714 only when clock cycles 2706 have become available. In FIG. 33 power management circuitry 708, in the MPU 102 of FIG. 7, has an output suspx control signal connected to the SUSP# input core circuit 702 of FIG. 7 to suspend operations therein when suspx is low. A high active Reset signal hreset from an input pin RSTCPU of MPU 102 is inverted low by an inverter 2802 which is connected to a first input of a NAND gate 2804 and thereupon forces the NAND gate 2804 to output a high which (buffered) is suspx high, preventing the MPU core clock from being stopped, and thus causing latches in the circuitry 701 to be clocked and thereby reset. The NAND gate 2804 provides a low suspx output to suspend the core clock when both the Reset signal is low and the output of an OR gate 2806 is high. A second input of NAND gate 2804 is fed by the output of the OR-gate 2806. OR-gate 2806 has a first input fed by the output of a NAND gate 2808 and a second input fed by the output of a dual-NAND flip-flop 2810. MAMD gate 2808 acts as an OR for low-active inputs. Notice that either of the inputs of OR-gate 2806 when high, and any of the inputs of NAND gate 2808 when low, can force suspx low to stop the core clock unless the RSTCPU pin signal hreset is active. A MASKCLK# low-active clock control signal from PPU 110 mask clock generator 2340 of FIG. 27 is fed to a corresponding input of MPU 102 and inverted to supply signal hmaskclk in FIG. 33 to a first input of a NAND gate 2812. When hmaskclk is low (in the part of its cycle that is to turn off the core clock), the output of NAND gate 2812 is forced high, whereupon it is inverted by an inverter 2814, the output 2816 of which goes to a first input of the NAND gate 2808 forcing the output of NAND gate 2808 high at OR-gate 2806 and ultimately producing a suspx signal low so that the core clock is indeed suspended. NAND gate 2812 has a second input fed by low-active control signal hsuspendx corresponding to the SUSPEND# input pin of MPU 102 fed by the SUSPEND# output of PPU 110. Thus, when hsuspendx is low, the core clock is suspended by suspx low unless reset is active. A test mode input nt01 is low in normal operation and qualifies a NOR gate 2822. The test mode input nt01 is high only in the test mode, but when this mode occurs, input nt01 via an inverter 2824 supplies a suspending low to a second input of NAND-gate 2808. Put another way, in test mode this input nt01 is high, stopping the internal CPU 701 core clock by driving suspx low. A third input of NAND gate 2808 is fed by the hresume signal of FIGS. 32 and 34. When this resume signal is low, indicating that the oscillator is not ready for normal use by the CPU, the suspx signal goes low unless reset is active. Before describing the circuitry associated with flip-flop 2810, a description is provided for the FIG. 33 suspend-control of the memory controller 718 of FIG. 7 via line 727 from power management circuit 708. The output (buffered) of NOR-gate 2822 supplies a signal hstoptomcu which when high disables or stops the memory controller 718. NOR-gate 2822 provides an ANDing of its low-active inputs hsuspendx, test mode nt01, and a control signal f_idle (inverted). The control signal f_idle (inverted) is an internal CPU 702 signal to which the CPU 702 suspend acknowledge signal SUSPA# is logically related (see hereinabove-cited TI486 Microprocessor: Reference Guide p. 1-9). Advantageously, this part of the embodiment arranges for suspend signal hsuspendx to sequentially 1) initiate suspension of the CPU 702 via logic 2804-2816; and then 2) subsequently suspend the operation of the memory controller MCU 718 via logic 2822-2828; and 3) finally generate signal hstoposc to stop the oscillator via further logic 2834. When f_idle goes high, with suspendx and nt01 low, the output of inverter 2828 goes low, indicating CPU suspend acknowledge, at an input of NOR-gate 2822. NOR-gate 2822 output hstoptomcu goes high to disable the memory control circuitry 718 of FIG. 7. The memory control circuitry 718 acknowledges by supplying a high signal hstopfmmcu (stop from mcu). A dual-NOR flip-flop 2830 has first and second NOR-gates 2832 and 2834 with the output of each NOR coupled to a first input of the other NOR. The output of NOR-gate 2834 is buffered to supply a signal hstposc (same as stop oscillator signal STOPOSC of FIG. 32) to the circuitry of FIG. 34 and the oscillator 706. Since this signal stops the oscillator itself as well as gating it, restart will take many cycles, and the oscillator will not be reliably available again until an active hresume signal (FIGS. 32, 33, 34) is received from the circuit of FIG. 34 for NAND gate 2808 of FIG. 33. As described, signal hstopfmmcu is connected as a set signal to a second input of first NOR-gate 2832, so that flip-flop 2830 captures a pulse of hstopfmmcu when such occurs. Signal hsuspendx SUSPEND# from PPU 110 is connected as a reset signal to a second input of second NOR-gate 2834 so that when a suspend is lifted by hsuspendx going high, the output of NOR-gate 2834 is forced low immediately and removes the oscillator stop. A power up reset signal pwrgood03 (see PWRGD3 in FIG. 21) is fed as an alternative reset signal via inverter 2836 to a third input of NOR-gate 2834, so that when power is coming on and lacks "good" status (pwrgood03 low), the inverter 2836 output goes high, forcing the output of NOR-gate 2834 low, and preventing the oscillator 706 from being stopped (or kept from starting) on power up. Refer now to a circuit section 2840 which provides an output on line 2841 to NAND-gate 2808. The input signals of circuit section 2840 are as follows: 1_regcoh6: a configuration register bit 6 establishes a clock mask via software entry in bit 6 hpclk: a high speed clock at half of crystal frequency (25 MHz with nominal 50 MHz. crystal) smi_in: a system management interrupt interlock hnmi: presence of a nonmaskable interrupt hintr: presence of any ordinary interrupt. The configuration bit six when high is turned into a low-active set pulse for flip-flop 2810 by being clocked by clock hpclk through two cascaded latches 2842 and 2844 to produce an inverted Qx output which is fed to respective first inputs of a NAND gate 2852. Configuration bit six itself is fed directly to a second input of the NAND gate 2852. The output of HAND gate 2852 is fed to a low-active set input of flip-flop 2810. The configuration bit six when low is converted into a low active reset pulse for flip-flop 2810 because the Qx output of the cascaded latches also goes to a first input of an OR gate 2854, and bit six goes directly to the other input of the OR gate 2854. This OR gate 2854 has its output low when both its inputs are low, thus providing a reset low to flip-flop 2810 via intervening gates 2864 and 2862. Power up reset signal pwrgood03 is fed to a low-active reset input of flip-flop 2810 and to a third input of NAND-gate 2852. In this way, when power is coming on but is not yet at "good" status, pwrgood03 is low and lifts any set input to flip-flop 2810 via AND-gate 2852 while resetting flip-flop 2810 at a reset input of the lower NAND gate thereof. An alternative source of low-active reset to flip-flop 2810 is provided by a NOR-gate 2862 which has three high active inputs responsive to interrupt hintr, nonmaskable interrupt hnmi, and the output of NAND gate 2864. For this purpose, NAND-gate 2864 acts as an or-function for three low active inputs: 1) smi_in, 2) hmaskclk (anded by NAND 2812 with suspendx), and 3) the output of OR-gate 2854 (configuration bit 6 low-active pulse when bit 6 goes low). The circuitry 2840 provides functions that confer system advantages. Among these advantages are, first, that setting configuration bit 6 high causes the CPU clock to be suspended via signal suspx except when an interrupt occurs, whereupon the interrupt is serviced by CPU activity with suspx lifted. Second, setting configuration bit 6 low lifts the suspension of core clock for activity in addition to interrupt service. Third, when PPU 110 introduces mask clock pulses (hmaskclk), the circuitry remarkably overrides a high configuration 6 without requiring a time-consuming software step of updating that register bit. This latter advantage is introduced by coupling the gates 2812 and 2814 for mask clock from PPU 110 back into the logic 2840 at gate 2864 to reset the flip-flop 2810 and lift the suspension imposed outside of interrupts. In FIG. 35, the process of operation introducing the mask pulses into circuit 2840 of FIG. 33 is shown step-by-step in waveform diagram form. In a first step "1" the register bit 6 is set high by software, causing a set pulse to flip-flop 2810 that takes line 2841 high and suspx low to mask the core clock. After an indefinite intervening time 3002, it is desired that PPU 110 start cycling the mask clock pulses instead of leaving the mask clock signal high. In a second step "2" the maskclk signal goes low, taking flip-flop line 2841 low via logic 2812, 2814, 2864, 2862 and 2810. Since mask clock low keeps the CPU core suspended via logic 2806-2816, this logic responds in third step "3" to confirmation of mask clock activity wherein mask clock goes back high, whereupon core suspend signal suspx goes high, lifting the suspend directly by mask clock activity and without any software intervention. FIG. 34 is a further schematic diagram of power management circuitry in the MPU for supplying a Resume signal hresume to the circuitry of FIG. 33. First notice that stop oscillator signal hstoposc (see also FIG. 33) when high during a time interval 2910 of FIG. 32 will force a NOR-gate 2902 output ENX low, which in turn forces resume signal hresume low via a NAND gate 2904 and succeeding inverter 2906. Resume signal hresume is variably delayed from the end of interval 2910 of FIG. 32 to its eventual return to high at transition 2714 by counter logic 2920 feeding a latch 2922 feeding a first input of a NOR-gate 2924 feeding a second input of the NOR-gate 2902. Power on reset signal pwrgood03 when high qualifies counter logic 2920 and further via an inverter 2926 qualifies NOR-gate 2924. Latch 2922 is clocked by a NOR gate 2923 which supplies a high transition to the clock input of the NOR gate 2923 when both 1x and 2x clocks become low. NOR-gates 2924 and 2902 also act together as a set-reset flip-flop with high-active output hresumel, wherein hstoposc is a high-active reset signal, and the output of latch 2922 is a high-active set signal. Note that hstoposc is the same as STOPOSC and HSTOPOSC of FIGS. 32 and 33. Start Count signal STARTCT is generated by a pulse former 2918 transitorily supplying a reset input to counter 2920 of FIG. 34 in response to a low-to-high transition of STOPOSC# (STOPOSC inverted) as indicated by the STARTCT label in FIG. 32. Release of SUSPEND condition (HUSPENDX low) in FIG. 33 can cause this STARTCT response, for example. In counter logic 2920, pwrgood03 and hresume low jointly act as an enabling signal, whereupon when the STARTCT transition in STOPOSC of FIG. 32 occurs, the counter 2920 (clocked by 1x pulses at nominally 25 MHz. from 50 MHz. crystal pulses divided by 2) starts to count up (or down) from zero or any suitable predetermined multi-bit value. During the count, the output 2921 of counter 2920 is low. This low is clocked through latch 2922, and NOR-gate 2924 output is high. At this time NOR gate 2902 output is forced low, inactivating the enable ENX (via an inverter) and holding the hresume signal low. In this embodiment, the circuitry of FIG. 34 is looking for a predetermined number of clock pulses 1x from the crystal oscillator before the oscillator is regarded as having successfully started whereupon hresume can go high. Notice that the pulses may be irregular in spacing at first, and the circuit simply counts the pulses that do occur. If the counter has not found the predetermined number within the about-30 microsecond period of the 32 KHz. clock, then that h32KHz. input resets the count. When the count in counter 2920 reaches at least a predetermined threshold value (e.g., 152) representing production of that many clock pulses by the 1x oscillator, its output 2921 goes high, latch 2922 output goes high, flip-flop 2924 output goes low whereupon NOR-gate 2902 output hresumel goes high (unless hstoposc goes active high to stop the oscillator). Note that the counter is suitably alternatively configured to count down to zero from a preset value. Attainment of the counting event causes enable signal ENX to go active (low) and enable block 3620 of FIG. 36 to output clock from MPU 102. Also, NAND gate 2904 becomes qualified by signal hresumel, and the output hresume goes high as soon as a stability signal stbl input to AND-gate 2904 goes high from a clock-doubling phase-lock loop (PLL) indicating the PLL has stabilized and is producing clock doubled clock pulses closely controlled in duty cycle value (e.g. 50%). FIG. 36 is a partially block, partially schematic diagram of a clocking and control circuitry embodiment of the MPU of FIG. 5, and should be read in conjunction with MPU FIGS. 9, 33 and 34. In FIG. 36, MPU 102 has block 701 including a 486 CPU core 702, a PLL 706, and the PMU 708 of FIG. 33. Outside block 701 and in MPU 102 is also memory control unit MCU 718, PCI bus bridge 716 and counter circuit 2900 of FIG. 34. PMU 708 has external terminal pin inputs for SUSPENDx and MASKCLKx, internal inputs FIDLE from CPU core 702, HSTOPFMMCU from MCU 718 and HRESUME from block 2900, and internal outputs HSTOP2MCU to MCU 718, suspend SUSP, and HSTOPOSC co oscillator OSC and counter block 2900. In an important improvement, clock buffer 3610 is interposed between PLL 706 output and the phase1/phase2 clock input of the CPU core 702. Output suspend SUSP from PMU 708 is fed to an enable input of the clock buffer 3610. This improvement confers advantages of suspending core 702 in one clock cycle, and subsequently resuming core 702 in one clock cycle. Resuming, which is a process step of returning to high speed clock operation after a suspend, advantageously can occur without a core reset and free of core register restore operations, since the core 702 has static circuits that retain their data even when the clock is suspended by PMU 708 and buffer 3610. The availability of this suspend mode saves power in coordination with the power management process and power management control circuitry 920 of PPU 110 responsive to the process and control circuitry 1620 in PCU 112. In MPU 102 a clock crystal X1 cut for 50 or 66 MHz for example, is connected via two pins to an on-chip oscillator circuit OSC which in turns provides an output OSCOUT to a divide-by-two clock divider 3615 which feeds a buffer 3617 that in turn connects to an input of an inverting clock buffer 3622 in a buffer block 3620. A second inverting clock buffer 3624 in said block 3620 is fed by a pair of cascaded inverters 3626 and 3628 supplied by undivided OSCOUT. Buffer 3622 has an output connected to a terminal pin of MPU 102 designated PCLKOUT (or OUT1X) which supplies the external clock buffer circuit 180 of FIG. 5. The circuit 180 shown in more detail in FIG. 36 has respective clock buffers which resistively drive the bus clock inputs PCLKA (pin PCLK) for MPU 102, PCLKB for PPU 110, PCLKC for PCU 110, PCLKD and PCLKE for devices 210 and 220 of FIG. 5 and PCLKF for display chip 114. Input PCLKA returns the MPU divided-by-two bus clock from buffer 3622 back into MPU 102 with timing essentially the same as for all the other chip clocks PCLKB-F, and clock skew in the system 100 is advantageously minimized. An internal inverting clock buffer 3631 fed by PCLKA supplies a clock HPCLK (host clock) to both the 1X CLK input of block 2900 and the HPCLK input of PCI bus bridge 716. Buffer 3624 supplies undivided clock to an output terminal pin for numerical processor unit clock NPUCLK of MPU 102 which is connected on printed circuit board 302 via a buffer in block 180 and resistance to FPU 108. This clock thus buffered is also returned via the resistance back to a terminal pin FB2 of MPU 102 and connected to the input of an inverting clock buffer 3633. The output HCLK2 of buffer 3633 is supplied to clock-multiplying PLL 706, MCU 718, PCI bus bridge 716 in MPU 102, and to the 2X clock input of counter block 2900. Counter block 2900 has input STBL connected to an output from PLL 706 indicating that the PLL has stabilized. The clock input CLK of block 2900 in FIG. 36 is marked CLK, is fed by inverter 3631, and is called "1X" in FIG. 34. Counter block 2900 is reset at input RST of FIG. 36 by 32 KHz. clock and as described in connection with FIG. 34. FIGS. 34 and 36 counter block 2900 output ENX is connected to both of two low-active enable inputs of inverting clock buffers 3622 and 3624 of buffer block 3620. Advantageously, the clock control provided by block 2900 ENX and buffers 3620 is responsive to the PCLKA input delayed by the external board 302 environment to stop and/or resume both the PCLKOUT and NPUCLK outputs generated internally in the MPU 102. In this way, timing is maintained and skew is minimized, while realizing single cycle stops and resumes for the whole chipset and system 100. FIG. 37 is a block diagram of frequency-determining crystal connections and clock lines in the system embodiment of FIG. 5-7. In FIG. 37 the clocking scheme includes four frequency-determining quartz crystals X1-X4. Crystal X1 is the nominally 50 or 66 MHz. crystal (much higher or lower frequencies also suitably used) connected to MPU 102. The PPU 110 has three crystals X2 at nominally 48 MHz, X3 at nominally 14.318 MHz. and X4 at nominally 32.768 MHz. All frequencies may be higher or lower for achieving the design purposes of the skilled worker in preparing various embodiments. When the system is in 5V SUSPEND, most of the subsystem clocks inside PPU 110 are disabled. The SUSPEND# input is used to generate a signal STABLEOSC which goes low immediately when SUSPEND# input is asserted, and goes high 58.6 milliseconds after the SUSPEND# input is deasserted. This signal is used to stop clocks to most of the subsystems of PPU 110. The delay of 58.6 milliseconds advantageously ensures that the oscillator output has been stabilized before the clock to different sub-blocks is strted. The disabling and enabling of the clocks is done in such a way that no glitches are produced, i.e. that a minimum pulse width of clock pulses is maintained. Further, any clock generated by PPU 110 that goes off chip has a signal that when stopped has a low logic level. Referring now to both the oscillator-related diagrams of FIGS. 37 and 24 (regarding circuits 920A, 920B), an OSCOFF signal is connected to a PWRDN pin of the 48 MHz. and 14.31818 MHz. oscillators. A STABLE14MHZ signal, indicating that the 14 MHz. clock has become stable, is generated to gate out the 14.31818 MHz. clock to an OSCOUT (also called OSC_CLK) pin. When the STABLE14MHZ signal is low the OSCOUT pin is held low, and when STABLE14MHZ signal goes back high, the OSCOUT pin starts generating 14.31818 MHz. clock again, without glitches. The STABLE14MHZ signal is deasserted low before OSCOFF signal is deasserted, and is asserted high after a STABLEOSC (OSC STABLE in FIG. 24) signal has been asserted. The 14.31818 MHz. OSCOUT clock is driven for about one hundred (100) milliseconds (msec) after the SUSPEND# signal is asserted to allow the VGA display subsystem to go through a power down sequence. Most peripheral subsystems do not require explicit clock control. Clock control, however, is described here for the floppy disk subsystem FDC/FDS. The clock to FDC/FDS subsystem is controlled by an FDCIDLE output of an FDC block. When the FDCIDLE signal is asserted, the clock to the FDC/FDS module is stopped. Clock is not stopped to the ECP parallel port or the serial port modules. The 32.768 KHz. clock runs continuously throughout the suspend/resume sequence and RESET stays inactive throughout. The external clocks PCICLK, KBRDCLK, 14.3MHz clock transition from full speed to zero or vice-versa. SUSPEND# is used to shut off all oscillators in the system except 32KHz. A clock signal SUS_32KHZ is a 32KHz clock signal supplied by PPU 110 to MPU 102 and used primarily for suspend mode DRAM 106 refresh timing. When SUSPEND# is lifted by a rising edge thereof, a circuit is enabled and produces a OSC 14MHZ STABLE signal after a predetermined number of 32KHz clock cycles that insures that the 14 MHz. oscillator has stabilized. PWRGD3 inactive immediately enables all stable clock outputs. The KBC_CLK output from PPU 110 is supplied to the keyboard controller and scanner. This clock is derived from appropriate frequency division from the 48MHz. crystal to produce any selected one of sixteen, twelve, eight, or four (16/12/8/4) MHz. clock rates, and its duty cycle is preferably kept near 50% (such as between 40% and 60%). FIG. 38 is a block diagram showing an interrupt routing system using one or more PCUs 112 connected to an interrupt routing circuitry embodiment in the PPU 110, with outputs for connection to the MPU, detailing the system embodiment of FIGS. 5-7. In FIG. 38, a system embodiment has a combination of the PPU 110 and one or more PCU blocks designated PCU 112.0,...PCU 112.n. The PPU 110 shadows the PCU 112 interrupt routing registers in block 1616. This circuitry overcomes problems existing heretofore. Software is written to route PCU card interrupts and Card Status Change interrupts to any of ten different standard PC interrupt lines, or channels. These PC interrupts are called IRQ3, IRQ4, IRQ5, IR17, IRQ9, IRQ10, IRQ11, IRQ12, IRQ14 and IRQ15. Other chips of this kind require a dedicated pin in the PPU for each such channel. This reduces the number of pins available on the PPU for other functions. The circuitry shown in Figure 38 permits the PCU 112.n interrupts to be transmitted to the PPU 110 chip using only three wires. The PPU monitors host processor writes to the PCU's internal registers and uses the information to route the three incoming interrupts to the ten standard PC-AT interrupts listed above. The three interrupt signals output by the PCU 112.n carry card status change interrupts, card A interrupts, and card B interrupts. If the PCU 112.n only supports two peripheral card slots then only two interrupt signals, one for card status change and one for card interrupts, would be needed. When the host system processor writes to one of the interrupt routing registers inside the PCU 112.n , the data is actually written to the corresponding register in both the PCU 112.n and the PPU110. When the host system processor reads from a routing register address, only the PCU 112.n responds and the PPU 110 remains inactive. In this way the contents of the routing registers in both chips is always the same and can be used by the PPU 110 to route the PCU 112.n interrupts. PPU 110 shadows some of the PCU 112 I/O registers that define PCMCIA compatible interrupt routing so that PPU 110 can route the interrupts internally to the appropriate interrupt request IRQ lines on behalf of each PCU 112. Three signals from PCU 112 to PPU 110 carry interrupt signals from PCU 112 card A circuitry, PCU 112 card B circuitry, and status interrupts from both card A circuitry and card B circuitry. Information stored in configuration registers in 1616 IGC and IGR for cards A and B respectively within each PCU 112 define how these interrupts are to be routed to any one of the ten possible IRQ lines of the AT type of IBM-compatible computer. For example, a modem interrupt request (IRQ) in an AT-system goes to a predefined IRQ line in the system, but another peripheral such as a hard disk drive goes to another predefined IRQ line. Since cards with different functions are or can be plugged at different times into the same PCMCIA card slot, the PCU 112 needs to sort out which IRQ line will carry the IRQ corresponding to the device in the card slot. PPU 110 also captures this information when it is being supplied along bus 104 to each PCU so that it is shadowed in corresponding registers CSINT3-0, CBINT3-0 and CAINT3-0, in register set 1222 in PPU 110 for each card A and B. These registers in register set 1222 correspond to the registers in register set 1616 as follows. ICR A and ICR B are shadowed in CSINT3-0. IGCA is shadowed in CAINT3-0. IGC B is shadowed in CBINT3-0. These registers in register set 1222 in PPU 110 enable the interrupt routing control circuitry 3820 inside the PPU 110 to route the interrupts to the IRQ lines of PPU 110 in the correct manner of the internally-implemented fast ISA (AT) bus inside the single-chip PPU 110. By loading in the Interrupt Control block 914 the identifier of the defined IRQ channel, as determined by the information stored in the shadow registers in register set 1222, the Interrupt Control block 914 is able to identify to MPU 102 the defined IRQ channel for the interrupt sent to MPU 102 on line INTR in response to the receipt of an interrupt from PCU 112.n in logic unit 3820, when subsequently interrogated by MPU 102 in accordance with conventional ISA interrupt signaling procedures. The PPU 110 identifies PCI I/O writes on bus 104 destined for the PCU 112 index and data registers at I/O addresses 3E0h (h=hexadecimal) and 3E1h respectively. If the index written to the I/O location 3E0h matches 03h, 43h, 05h, or 45h, representing the addresses of CAINT3-0 (03h), CBINT3-0 (43h), and CSINT3-0 (05h and 45h), the data written to data register 3E1h is stored internally in the corresponding register in register set 1222 by the PPU 110. This information is used to control the interrupt routing as described below. This information can be read back from PPU 110 at PCI base address 50-51, as described in connection with the PCU Interrupt Shadow Register. Note that the PCU Interrupt Shadow Register in 1222 is updated every time the corresponding PCU 112 registers in 1616 are written, using I/O accesses, without handshaking to the PCI bus as would be the case in a PCI transaction, but the register can also be updated by directly writing to PPU 110 configuration base address 50-51, recognized by I/F block 902. Any previous shadowed information is thereby lost. In this way PCMCIA Card Services and Socket Services software (that may prefer to program PCU registers via PCI configuration cycles) advantageously can write appropriate interrupt routing information to the PPU interrupt routing control register. Some configurations of the PCU 112 allow it to reset some of its registers and to disable interrupt routing automatically when a card such as card A or B is removed from a socket. Since the PPU 110 cannot determine whether a PCMCIA card has been removed from a PCU socket, it would not disable interrupt routing automatically. The system therefore appropriately generates a Card Service interrupt CRDSRVRQ when a card is removed, and the interrupt service routine in software suitably is programmed in a process embodiment to include a process step implemented in computer code to disable the interrupt routing inside the PPU 110. In the tables in this Detailed Description for the PCU 110 registers, the Interrupt and General Control (IGC) Registers are 8 bits each for each card A or B. The LSB four bits CINT3-0 in IGC-A select the routing for PC card I/O interrupts for card A. The LSB four bits CINT3-0 in IGC-B select the routing for PC card I/O interrupts for card B. Analogously, the Card Status Change CSC Interrupt Configuration Registers ICR are 8 bits each for each card A or B. The LSB four bits SINT3-0 in ICR-A select the routing for CSC interrupts for card A. The LSB four bits SINT3-0 in ICR-B select the routing for CSC interrupts for card B. Tables for the interrupt routing configured by the codes in each of this four bits CINT3-0 for A and SINT3-0 for A, and likewise for B are shown in tabulations 0000-1111 embedded for those bits in the larger charts elsewhere herein describing the IGC and ICR registers. When PCU 112 is used as a standalone device in a computer system, it suitably routes status change interrupts from card A and card B onto respective selections through selector mux 3810 to ten interrupt lines and pins shown in FIG. 38 as IRQ 3,4,5 plus seven Other IRQs. However, when the PCU 112 is used in the environment of system 100 as diagramed in FIG. 38 and called a Chipsetname environment (Chipsetname Enable bit = = 1), the three interrupt outputs from FIG. 31 XNOR gates 2692, 2694, 2696 are advantageously routed directly through selector 3810 to three corresponding predetermined IRQ pins, here IRQ3,4,5. The Chipsetname Enable bit is bit zero (0) in the Initialization Register tabulated with the Extension Registers for PCU 112 elsewhere herein. When this Chipsetname Enable bit is reset by default or by software to hold a value zero, then the standalone device mode for selector mux 3810 is selected. The PPU 110 shadows the PCU 112 register locations that define status change interrupt routing for both card A and card B, but internal to the PPU 110, only one shadow register (the PCU Interrupt Shadow register in 1222 of PPU 110) is maintained in the preferred embodiment. As a result, if PCU 112 were set up to route card A and card B status change interrupts to separate IRQ lines, the PPU would only respond to the interrupt routing request that was most-recently programmed. For example, if PCU 112 is programmed to route card A status change interrupts to IRQ4, and later, card B status change interrupts are routed to IRQ7, the PPU 110 routes all the status change interrupts to IRQ7. However, current PCMCIA Card Services and Socket Services software is expected to write the same value to both register ICR A and ICR B. In any event, in this way, the important system information that at least one card has had a status change is efficiently routed to the PPU 110 with only one line for card service interrupt request CRDSRVRIORQ. The SMIEN bit (Bit 4) of shadowed exchangeable card architecture offset location 03h, 43h determines whether the PCU 112 card status change CSC interrupts are routed to SMI pin of the PCU 112, or to AT-compatible IRQ pins. If AT-compatible IRQ routing is selected, then the SINT3-0 bits (bits 7,6,5,4 (7:4)) of the IGR registers (registers 05 and 45) determine how card status interrupts are to be routed, as shown in the SINT3-0 table for those registers. FIG. 39 is a waveform and process of operation diagram for selected signals in logic circuitry 3820 of FIG. 38 responsive to the three interrupt requests for Cards A and B and Card Service. Logic 3820 supplies these signals to a selector mux 3830 which routes the three interrupts according to the shadowing information CSINT3-0, CBINT3-0, CAINT3-0 to interrupt controls as shown in FIG. 43. Since the three interrupt requests may have unpredictable length, and the interrupt circuitry advantageously uses signals of predetermined length, the logic 3820 is responsive to produce a signals, such as signal QA, of predetermined length for card A, and analogous signals QA for the other two interrupt requests CRDBIORQ and CRDSRVRQ. FIGS. 40 and 41 describe processes of operation for fair rotation in arbitration by arbiter 906 described elsewhere herein in connection with PPU 110 of FIG. 11. FIG. 42 is a more detailed block diagram of a fast internal PPU bus 904 with parallel port 938 embodiment of the PPU of FIG. 11, as described elsewhere in connection with that parallel port 938. Note that the pinout to external terminals is elsewhere tabulated for the parallel port interface 4245. The description here concentrates now on the connections to the interface 4210 to on-chip improved Fast-AT bus 904. Two sets of 16-bit data sub-buses SDO and SDI are respectively specialized to carry input on bus SDI to inputs SDI15-0 of I/F 4210, and to carry output from I/F 4210 to the lower byte lane SDO7-0 of bus SDO. Data is transferred between SDI and SDO data buses by SDI/SDO interface I/F 4250. The SDI data bus is connected to reflect the state of any external inputs and of any internally-generated SDO bus outputs sent externally. By contrast, when the SDO data bus carries internally generated signals to internal destinations, the SDI and SDO states will differ. This arrangement advantageously eliminates much three-state circuitry in one embodiment. In this way, not only is the clock speed of bus 904 higher than in a corresponding AT-type external board-based bus, but also the width of the data bus is doubled, due to the on-chip implementation of bus 904 and the peripherals connected thereto in FIG. 11 and 42. Control CTRL lines for I/O read IOR# and I/O write IOW# connect to I/F 4210. Three address lines SA2-0 from the SA address sub-bus of bus 904 are also supplied as address inputs to I/F 4210. Chip select signals for parallel port chip select PPCS# and extended capabilities port ECP chip select ECPCS# are decoded by block ADR DECODE from the full width of SA bus. DMA request PDRQ is connected from I/F 4210 of the parallel port to the DMA block, and the DMA acknowledge line PDACK# returns from DMA to I/F 4210. A parallel port interrupt request line PIRQ also is provided. Clocking by SYSCLOCK is provided. Data router 1210 is fed signals from I/F 4210 for parallel data output enable PDOEN# and parallel port read enable PPRDEN#. FIGS. 43 and 44 are more detailed block diagrams of interrupt routing circuitry as described elsewhere in connection with the PPU interrupt block 914 of FIG. 38. Interrupts from ISA cards in a docking station 7 of FIGS. 70 and 65 also are communicated serially to and output from a sideband serial port 7010 in PPU 110. These interrupts IRQx are routed via interrupt router block 3830 to the particular IRQ-numbered interrupt input line (to controller 914) to which the identity of each ISA card corresponds under ISA technique. This routing is established in a first embodiment by simply jumpering the ISA cards in the docking station in a predetermined manner and then OR-ing all IRQx lines in block 3830 to the corresponding IRQ-numbered input line of controller 914, provided the routing of card A, B and Card Service interrupts can be known or characterized beforehand. In a second embodiment, an additional control register set up by BIOS from bus 904 supplies control information for this routing, and routing circuitry 3830 is responsive to the control information to keep any two interrupts from the docking station and the PCU 112 from driving the same IRQ-numbered input to controller 914. FIG. 45 is a flow diagram of a process or method of operation of the preferred embodiment system of FIGS. 5-7. In FIG. 45, PMU (Power Management Unit) hardware in PPU 110 notifies BIOS software 4510 of system management events by sending SMI interrupts to MPU 102 which executes the BIOS software 4510. BIOS software sends commands by programming the configuration registers 712 of MPU 102, 1222 of PPU 110, 1616 of PCU 112, and configuration registers in each of the other devices connected to bus 104. An operating system (OS) 4520 such as DOS or WINDOWS or any other operating system having a power management feature polls events from information supplied by BIOS 4510, and returns a CPU IDLE notification to the BIOS 4510. The operating system provides notification of system events to Applications software 4530. Either or both of the OS and/or the Applications provide interrupts to power management software 4540. Power management software 4540 provides an output for T(on)/T(off) adjustment of the TONTOFF register in PMU 920 hardware of PPU 110. Advantageously, the embodiments described herein are compatible with passive and active power management algorithms. Passive power management algorithms reactively adjust the CPU clock based on system activity (inactivity) timers such as those of FIG. 25. Active power management algorithms estimate CPU activity, and can be adaptive in nature. FIG. 46 is a flow diagram of a process or method of operation for power management adjustment of a TONTOFF register of FIG. 27 in the preferred embodiment system of FIGS. 5-7. After BEGIN and an initialization of the TONTOFF to an initialization value such as 50% duty cycle in a step 4605, operations go on with a test step 4610 for system idle status, which is repeated until an idle status is found, whereupon operations proceed to a step 4620 to check for 55 ms. timer tick interrupt IRQ0. When that interrupt is detected, operations go on to a step 4630 to monitor the keyboard, mouse, display VGA, hard disk, timers and status counters of PMU 920 in PPU 110 as well as activity timers in PCU 112. In this approach, the high 4 bits (or all if desired) in each of the eight counters of FIG. 25 are concatenated and read via bus 904 by software according to step 4630 periodically (e.g. on each IRQ0 DOS timer tick). Next in a step 4640, the process computes a criterion function F of the values in the timers and counters. One example of criterion function F is a minimum (min function) of various values in the timers suitably weighted. FIG. 47 shows a structure for supplying data for a version of this approach, wherein the listed system trigger signals of FIG. 47 are suitably selected or masked by software write to mask registers 4710, and then the selected (unmasked) trigger signals are ORed together by an OR-gate 4715 to a common TRIGGER reset input of a counter 4720. Note that any FIG. 47 monitored or unmasked system activity between consecutive keystroke trigger events also produces a trigger of its own to freeze the counter for a read and subsequent reset at input RESETB and restart by gating in the CLOCK. Thus, the counter combines system information for all unmasked system sources to prpvide a time between any event and the next event which may be of the same type or another type of system event. The value in the counter upon each trigger event is read over data bus 904 by software of step 4630 and translated in step 4640 to provide the function F latest value. Since some scattering or variability of counter data in this approach is to be expected even in a system steady state, some averaging of plural successive counter values is utilized in an example embodiment. Some low predetermined value in counter 4630 is translated to be the function F zero value or low threshold ThO. Some higher predetermined value, or the maximum value that counter 4630 can have, is translated by subtraction and scaling to be a halt threshold or high threshold Th1 (scaled to be unity, for example). Another example of a criterion function F for step 4640 is a weighted sum of the values in the timers, with the weights determined so that the process operates to minimize power consumption. A special case of the weighted sum concept applies zero weights to (or ignores) some timers. A simple special case simply monitors the VGA timer of FIG. 25 to follow keyboard and mouse activity. In a succeeding test step 4650, the criterion function F value computed in step 4640 is compared with a predetermined first threshold value such as zero. If the criterion value is less than the first threshold value (YES condition) due to substantial user demand and system activity causing low elapsed times in the timers of FIG. 25 for example, then operations loop from step 4650 back to step 4610 via a recordkeeping step wherein a note is made that the criterion value is deemed to be equal to the first threshold value (e.g. 0). However, if the criterion value F exceeds the threshold value due to low user demand (e.g. no keystrokes and mouse activity) and low system activity, then operations instead proceed from step 4650 to a step 4660. In step 4660 the criterion function is compared to a second threshold value to determine whether the system should merely be slowed down, or should be halted. If system activity is so low that very long timer values are occurring on all the timers, for example, then operations proceed to a step 4670 to initiate a halt, such as to actively cause entrance to a Suspend state or mode by writing to bit 13 (SUSPBTN) of register SOURCE_SMI to simulate the use of the Suspend Button 32. Then in a step 4675, recordkeeping sets Fo to a deemed value equal to the second threshold, or halt number of step 4660, whence operations loop back to step 4610. If in step 4660 criterion value F is insufficient to justify halt, operations branch to a step 4680 to update the TONTOFF register 2510 in FIG. 27. The updated value is determined according to a selected computation which provides one or more advantages such as stability of computed result in a system stead-state, freedom from hunting or erratic behavior in the TONTOFF value, relative speed of adaptation to new conditions, reduction in power consumption, user convenience, and at least approximate and preferably very close to optimum power management control. In a first example, the updated value is computed as TONTOFF = [(Th1 - F)/(Th1 - Th0)] x 128, where Th1 is the halt number threshold of step 4660 and Th0 is the criterion first threshold (e.g. 0) of step 4650. So when Th0 is zero, the second example update value is one minus ratio of criterion function F divided by Th1. This first example provides all the above-listed advantages and trades off a little smoothness in change for speed of change because one value of F is used. In a second example, an averaging filter process is employed wherein the current F value and the recordkeeping value Fo are averaged and used in place of F in the equation (1) of the first example: TONTOFF = {[Th1 - (F+Fo)/2]/(Th1 - Th0)} x 128 This second example provides all the above-listed advantages and trades off a little speed of change for more smoothness of change because two values of F are used. More F values windowing n loops of the process 4540 can be used if the greater complexity of computation and reduction in speed of change are acceptable. The process of these examples responds to sensors of system activity to produce one or a plurality of values between first and second threshold values and representative of system activity and then repeatedly generates a control value representative of duty cycle in clock masking, as a function of the one or a plurality of said values, whereupon a clock masking circuit continually responds to the control value to establish and continually modify the clock masking function to power-manage the operation of the system. To achieve adaptive CPU clock control, the thresholds Th0 and Th1 and/or the criterion function F itself are dynamically adjusted based on errors in CPU activity prediction. Following the TONTOFF update of step 4680, operations pass to a recordkeeping step 4685 where recordkeeping value Fo is given the current value of criterion value F, whereupon operations loop back to step 4610. In a simple example, let Th1 = = 1, Th0 = 0 without loss of generality. Let recordkeeping value Fc = 0 initially, TONTOFF = 50%, and F is first computed as 0.4 perhaps largely determined, for example, by a series of user keystrokes at a slow rate. Using the formula of the second example, TONTOFF = {[1 - (.4 + 0)/2]/(1 - 0)} x 128 = 102 (decimal) In a next loop through process 4540, Fo = .4, recordkeeping on the first value of F. Now suppose the system adjusts and operates and a new value of F comes in at .6 indicating the slowdown. Now the second iteration on decrement becomes TONTOFF = ([1 - (.4 + .6)/2)/(1 - 0)) x 128 = 64 (decimal) Thus, process 4540 implements a servo loop that homes in on an optimum behavior that varies over time for TONTOFF and thus for the power management of the system that satisfies user demands. Different versions of process 4540 that use other servo loop or filtering formulas and steps are contemplated where these provide faster control behavior or otherwise tune the power management system. FIG. 49 shows a structural diagram of an adaptive CPU clock control for power management. Various observations such as counter and timer values are obtained by sampling or sensing these values over time. Either hardware or software can provide the functions of observation and sampling in system, device, and process or method embodiments. In the process or method embodiment of FIG. 46, the sampling and observation occur in monitoring step 4630. Next the values or samples thus obtained are weighted in hardware or weighted by computation as described in connection with step 4640 of FIG. 46. Then these values are provided to a filter or servo structure. FIG. 46 implements this operation as the rest of the steps in the process loop 4540. FIG. 47 is a block diagram of a system activity timer embodiment alternative to the embodiment of FIG. 25 as described above in connection with FIG. 46. FIG. 48 is a block diagram of a keyboard polling monitor circuit embodiment for use to supply a trap signal to the SMI circuit embodiment 2370 of FIG. 28. In FIG. 48 a counter 4810 is clocked by the output of an AND gate 4820 fed by keyboard chip select signal KBCS and an SA2 address input from bus 904. The counter 4810 counts the transitions at the clock input, and is read for power management purposes on bus 904 upon assertion of a Read Keyboard Polling Monitor READKPM# to an output enable input of counter 4810. Also, for SMI purposes, all but a selected bit of counter 4810 are masked off so that the bit is fed to SMI circuit 2370 so that the bit is advantageously used for SMI purposes as well. Further in FIG. 48, the count is reset in counter 4810 by an OBF output from keyboard controller 118 fed to a clean-up latch 4830 via XD bus 116 of FIG. 6. The cleaned up OBF output of latch 4830 is supplied to a first input of a NOR gate 4840 the output of which is connected to low-active reset input RST# of counter 4810. The second input of NOR gate 4840 is fed from a clock of suitably long period to act as a default reset source in case OBF does not reset the counter. FIG. 49 is a block diagram of an adaptive CPU clock control system and method for power management as described above in connection with FIG. 46. FIG. 50 is a schematic diagram of a system environment sensing circuit. In FIG. 50 a system environment sensing circuit 3400 has a reference voltage supply 3410, a 3.3 volt power-good sensor 3420 and a 5 volt power-good sensor 3430 (all in supply 172), and an analog comparator 3440 (in temperature sensor 140). Reference voltage supply 3410 has a pair of diodes 3411 and 3412 with their anodes respectively connected to 5 volt and 3.3 volt sources and with their cathodes connected together and to an electrolytic capacitor 3413 to supply a comparator circuit supply voltage VCOMP. A reference voltage VREF which is less than VCOMP is developed by a dropping resistor 3416 series connected to an avalanche diode 3418 across the electrolytic capacitor 3413. A capacitor 3417 is connected across the avalanche diode 3418. The anode of the diode 3418 is connected to ground, and the cathode thereof is connected to a line to supply reference voltage VREF. 3.3 volt power-good sensor 3420 has a comparator operational amplifier 3452 with its noninverting (+) input connected to a voltage divider 3454 fed from 3.3 volt supply voltage. The inverting (-) input of op amp 3452 is connected to reference voltage VREF. Op amp 3452 has voltage VCOMP as its supply voltage, has its output connected to the PWRGD3 output line, and has a hysteresis resistor 3456 connected between its output and its (+) input. A switch 3460 forces the input to zero volts for disabling or test purposes. A 5 volt power-good sensor 3430 has the same internal circuit as shown for sensor 3420, so that circuit shown in block for brevity. A switch 3465 independent of switch 3460 forces the input low on the op amp in sensor 3430 generating system wide resets for 3.3 and 5V power planes. The output of sensor 3430 is power-good 5 signal PWRGD5. In temperature sensor 140 a temperature-responsive element 3470 such as a thermistor is thermally contacted or thermally conductively affixed to the chip package 3475 of MPU 102 that is attached to PCB 302. In another embodiment element 3470 contacts inside the package 3475 itself to the actual substrate of MPU 102 integrated circuit physically located in the package. A five volt supply voltage is connected by a jumper across a voltage divider comprising thermistor 3470 in series with a resistor 3477. The inverting input of an op-amp 3440 is connected to receive divided voltage from the connection between 3470 and 3477. The noninverting input of op-amp 3440 is resistively connected to reference voltage VREF by a resistor 3483. A hysteresis resistor 3481 links the output of op-amp 3440 with its noninverting input. The output of op-amp 3440 supplies the low active output TEMHEAT# to FPGA 124 of FIG. 6 and is connected to a pullup resistor 3479 to VCCXD supply voltage for the XD bus circuitry. The advantage of hysteresis resistors 3456 and 3481 in FIG. 50 is to create a first threshold before the active signal is given, and then create a second threshold to which the condition must retreat before the active signal is inactivated. This promotes stability in circuit operation and system control. FIG. 51 is a block diagram of power supply connections for a system of FIGS. 5-7. Note further that PPU 110 has different VCC voltage levels on the same die as described in connection with FIG. 55. A standard AT-computer type power supply connector 5110 supplies voltage lines and supplies a 3.3v. linear regulator 5120 to provide VCC_3. A battery power supply connector 5130 has lines for 5V, 3.3V, and 12V for LCD control, EPROM programming, and voltages for MPU 102, PPU 110, PCU 112, VGA 114 and the other chips in system 100, supplied to a set of jumpers 5140, manual switches, or a software programmable VCC switch so that each voltage source and line intended for the various chip VCC destinations is effectively routed thereto. See the pinout tabulations for MPU, PPU and PCU, and the VCC tabulation in connection with FIG. 55. FIG. 52 is a partially block, partially schematic diagram of a power supply circuit for PCU 112 in the system of FIGS. 6, 8, 20 and 21. In FIG. 52, supply voltages 3.3V, 5V, and 12 V are distributed under the control of PCU 112 using a commercially available TPS220X circuit. A jumper block JP5 (or software programmable power switch) selectively routes 3.3V or 5V to U11, and alos to the VCC pin of PCU 112 along a line POWER1 which is suitably RF-bypassed by capacitors 5210. Voltage programming outputs of PCU 112 for card A or B are the same as the corresponding inputs of U11 marked on FIG. 52, see also pinout tabulation and FIG. 18. Card A and B supply voltages AVCC and BVCC are supplied by circuit U11 both to PCU 112 and to the upper and lower level card connectors A and B of connector 306 of FIG. 8. Card A and B programming voltages AVPP and BVPP are supplied by chip U11 to the upper and lower level card connectors A and B. VPPGOODA# and VPPGOODB# outputs of circuit U11 connect respectively to pin inputs A_GPI and B_GPI of PCU 112 which are described further in connection with PCU 112 elsewhere herein. The SUSPEND# line of FIG. 20 from PPU 110 is fed to a low-active Shutdown input SHDWN# of circuit U11. Because circuit U11 of FIG. 52 cooperates closely with PCU 112 in this embodiment, they are shown in one block 112, U11 of FIG. 20. FIG. 53 is a block diagram of a CPU-clock-rate temperature sensing and control circuit embodiment for implementation in MPU 102 or PPU 110 of FIG. 6. The illustration shows MPU 102 as the site, for example. In FIG. 53, the CPU clock CPU_CLK of FIG. 36 (also designated as PH1/PH2 output of buffer 3610) is fed to a temperature sensing circuit 5300 which advantageously monitors the actual MPU 102 activity. Circuit 5300 has a counter 5310 which is cocked by CPU_CLK and provides clean outputs to a Latch A 5315. Latch 5315 is clocked by 32KHz. clock, while counter 5310 has its reset input connected to sufficiently delayed 32KHz. clock to allow Latch A to capture the count before counter 5310 starts over. The number of bits N in the counter 5310 is at least such that 2-to-the-N-power is about the same as or greater than the ratio of the CPU nominal core clock frequency at 100% MASKCLK duty cycle to the frequency of the counter reset clock (here 32KHz.). For a 66MHz. CPU clock and 32KHz. reset clock, the ratio is 2062, close to 2048 or 2-to-11th power. Therefore, counter 5310 is at least 11 bits long in this embodiment. The reset clock is set high enough to conserve counter bits in 5310 and low enough so that a substantial sample of CPU clock pulses is taken. A Threshold Register B 5317 is loaded from local bus 714 (FIG. 9) with a value indicative of the number in latch A 5315 which would keep the temperature of MPU 102 constant, considering the ambient temperature, thermal resistance and convective cooling level for MPU 102. Next a subtractor unit 5320 outputs the difference A-B of the contents of Latch A and Latch B to an accumulating circuit 5330 which keeps a running total of entries, and which is limited to positive values, and zeroing on negative totals (but not merely negative inputs). The contents of accumulator 5330 model the temperature of MPU 102 rising and falling with activity level. The output of accumulator 5330 is supplied to each operand A input of a pair of comparators 5340 and 5345. Over/Under temperature limit values supplied by software via bus 714 are loaded into respective registers 5350 and 5355 which in turn respectively feed the B operand inputs of comparators 5340 and 5345. A comparator 5340 A greater-than B logic level output and a comparator 5345 A less-than B logic level output are respectively fed to the D data inputs of a pair of one-bit latches 5360 and 5365. These two bits TEMP_HIGH and COOLED-DOWN respectively are readable on bus 714 by power-management software. Accumulate circuit 5330, and latches 5360 and 5365 are clocked by 32KHz clock. If an over temperature condition occurs, as indicated by an active one TEMP_HIGH for example, the power management software or PMU 920 hardware executes a process or method by which it issues a SUSPEND# signal to cool off MPU 102 until the COOLED-DOWN bit goes high and the TEMP_HIGH bit goes low, whereupon the system 100 is resumed. Compared to the TEMHEAT# circuit of FIG. 50, the circuit embodiment of FIG. 53 provides advantages of programmable hysteresis levels in rgisters 5350 and 5355, as well as direct electronic sensing of the electronic circuit without actual thermal contact. On the other hand the TEMHEAT# circuit of FIG. 50 provides advantages such as direct thermal contact which inherently takes account of ambient temperature, chip activity, thermal resistance and convection level without special modeling circuitry 5310, 5315, 5317, 5320, 5330. FIG. 54 is a block diagram of another temperature sensing and control circuit embodiment 5400 for implementation in MPU 102 or PPU 110 of FIG. 6 and having fewer blocks. Local bus 714 can write to Over Temp register 5350 and Cooled Down Register 5355, and can read output bits for Temp High and Cooled Down. In FIG. 54, 32 KHz. clock is divided by a frequency divider 5415 which rolls over and triggers a one-shot pulse generator 5417 to periodically supply a Load signal to a LOAD terminal of a counter 5410 whereupon the over-temp register 5350 value is loaded into counter 5410. The high speed CPU clock CPU_CLK clocks counter 5410 in a down-counter mode. If counter 5410 counts so many clock pulses that it counts down to zero, a BORROW output goes active and clocks a latch 5420. Latch 5420 has its D input tied high, so that after occasional software polling reset R, a BORROW output passes the high D input to the Q output to actively indicate a TEMP_HIGH condition. A frequency divider 5425 down-count clocked by 32KHz, a latch 5430 fed by divider 5425 Borrow, and Cooled Down Register 5355 for loading divider 5425, provide a programmable timing circuit which is activated by or when TEMP_HIGH active at latch 5420. In this way, a programmable time elapses upon TEMP_HIGH going active before a COOLED_DOWN output of Latch 5430. Power management software or hardware resets latches 5420 and 5430 in some system, device and method embodiments. Also, the reset is derived from the COOLED-DOWN output in another embodiment. FIG. 55 is a schematic diagram of a circuitry embodiment for reducing power dissipation at a boundary between differing-voltage areas 920A and 920B of the PPU 110 also shown in FIGS. 6, 11, 12, and 20-22. Dual voltage VCCs coexist on the same silicon device (such as PPU 110) to enable low power, multiple supply voltages and regions associated therewith to be integrated on the same device substrate. The die is physically sectioned into different VCC wells or regions, and a special dual voltage interface circuitry 5515 is used at the boundary each of pair of VCC wells 5510. For a single-VCC device, a ring of VCC and ground GND is provided around the I/O buffer area at the periphery of the die or chip. For multiple VCCs, the VCC ring is segmented into different pieces, and the GND ring remains continuous or unsegmented. In the exemplary embodiment of PPU 110 in FIG. 12 several rings are used: V_3: 3.3 volt supply for PMU 920A (unless 5v. used), PCI/AT I/F 902, 906, central region for 910,914,916 V_XD: 3.3V/5V selectable voltage for XD port V_DK: 3.3V/5V selectable voltage for IDE IF/FDC 932, 934 V_5: 5V supply for SIU 936 and PIU 938 and also for PMU 920A if 3.3 volts is not used for PMU 920A V_bat: 3 V battery supply for PMU 920A, RTC 918 and RAM 919 Pin numbers intermediate on the edges of the PPU 110 die of FIG. 12 indicate specifically where the breaks of the VCC ring occur in terms of I/O site location. For a single-VCC device a grid of VCC and GND suitably exists in the core of the device and not in the I/O buffer strip area around the edges of the device. For multiple VCCs, the VCC grid is suitably isolated into regions respective to each tabulated "V_" VCC above, advantageously preventing power supply shorts. In the next description, a boundary between a 5 volt VCC PMU 920A and a 3.3 volt battery powered PMU 920B is used as an example. Another equally applicable area is the boundary between the 3.3 volt central region for 910, 914, 916 and the adjacent 5 volt region for SIU 936, PIU 938 and the adjacent selectable 3V/5V region for FDC 932, IDE I/F 934. In FIG. 55, an inverter 5512 with 5 volt VCC feeds an inverter 5514 with 3.3 volt VCC in a signal path leading from higher supply voltage VCC section 920A to lower VCC section 920B. In an opposite path, an inverter 5516 with 3.3 volt VCC would, without more, feed an inverter 5518 with 5 volt VCC in an internal signal path INT leading from lower supply voltage VCC section 920B to higher VCC section 920A. Signal swing on the 3.3 volt inverter 5516 would be insufficient to prevent high current events in the 5 volt inverter 5518 wherein an upper p-channel FET therein is partially on, and a lower n-channel FET is also partially on. The embodiment in FIG. 55 avoids such power-wasting and heat dissipating behavior, first, by providing a positive feedback circuit or element on the device 5518 on the higher VCC side of the boundary 5510. Such circuit is suitably, for example, a p-channel FET transistor 5520 having a gate connected to the output of inverter 5518, and the source and drain terminals thereof connected between the 5 volt VCC and the inverter 5518 input. An additional device 5522, suitably an open-collector (OC) or open-drain inverter, is provided between the output of inverter 5516 and the input of inverter 5518. An n-channel FET 5524 cooperates with OC device 5522 and assists high-to-low transitions at the input of high VCC inverter 5518. FET 5524 has its gate connected to the output of inverter 5518 and its source-to-drain path connected between inverter 5518 input and GND. Inverter 5516 high-to-low transition drives a 3.3volt inverter 5526 which in turn drives an "open-collector" (single n-channel FET) inverter 5528, which in turn drives the output node of inverter 5518 and the gate of FET 5520 low. In this way, a high-to-low transition at inverter 5516 output pulls down the inverter 5518 output node so that transistor 5520 advantageously pulls the signal INT all the way to 5V. Conversely, a low-to-high transition by inverter 5516 pulls the input of inverter 5518 low via "open collector" inverter FET 5522, whereupon inverter 5518 output starts to go high, turning on the feedback transistor 5524 and accelerating the low-to-high transition at inverter 5518 output with greatly reduced power dissipation. The OC inverters 5522 and 5528 are sized sufficiently large relative to FETs 5520 and 5524 to drive the operations described herein. This arrangement provides good performance even if the 5V region 920A has its VCC changed or switched to 3.3V or even a lower voltage. A NAND gate 5530 feeds a NOR-gate 5532 in a high-to-low VCC path straddling the boundary 5510. No special feedback elements are applied to either of these two gates in this embodiment even when gate 5532 has other inputs such as 5534 from the higher VCC side and 5536 from the lower VCC side. However, low-to-high VCC circuits straddling the boundary have feedback elements applied as with block 5515 and as further described next. A lower VCC NAND gate 5542 feeds a first input of a higher VCC two-input NAND gate 5544 on the 5 volt side. Accordingly, a power reduction circuit 5515A identical to circuit 5515 is interposed between the output of NAND gate 5542 and the first input of NAND gate 5544. A lower VCC NOR gate 5548 feeds a second input of the higher VCC two-input NAND gate 5544 on the 5 volt side. Accordingly, a second identical power reduction circuit 5515B is applied between the output of NOR gate 5548 and the second input of NAND gate 5544. Next it is hypothetically intended to drive three inputs of high-VCC NOR-gate 5560 respectively with 1) a low-VCC NOR-gate 5552, 2) a low-VCC NAND gate 5554, and 3) a low-VCC inverter 5556. Higher power dissipation is prevented by interposing circuits 5515C,D,E (identical to 5515) between the lower VCC gates 5552,5554,5556 and the 3 inputs respectively of high-VCC NOR-gate 5560. The output of NOR-gate 5560 is coupled back across the boundary 5510 to feed an input of a lower-VCC two input NAND gate 5570 without further feedback provision. In FIG. 66, a lower VCC open collector inverter 6610 has its gate connected to a signal IN. A source-drain path of FET 6610 is connected in series with the source-drain path of another FET 6612 to feed higher VCC inverter 6620 across boundary 5510. Since inverter 6610 is open collector it can pull down the INT signal causing inverter 6620 to make OUT go high. Advantageously, another open collector inverter 6640 and enabling transistor 6642 cooperate in the other direction and pull up the INT node as next described. FETs 6612 and 6642 both have their gates connected to an enabling signal EN which when active renders them conductive. An inverter comprised of pmos FET 6630 and nmos PET 6635 has both gates connected to OUT and to the output of open collector inverter 6640 via FET 6642. The source and drain of FET 6630 are connected between the INT node and 5V VCC, and the source and drain of FET 6635 are connected between the INT node and GND. Another inverter 6650, having upper and lower FETs therein, has its input connected to the input IN of OC inverter 6610. Inverter 6650 has its output connected to the gate, or input, of OC inverter 6640. When IN is going from high to low, inverter 6610 is off and the output of inverter 6650 goes high, taking the output of OC inverter 6640 low which forces the output OUT low via transistor 6642 directly. This also causes transistor 6635 to shut off, and transistor 6630 to conduct, therefore pulling the signal INT to the higher VCC 5V supply voltage and causing higher VCC inverter 6620 to output a hard low. Advantageously, the principles and circuits disclosed in FIGS. 55 and 66 as examples above confer power-reduction improvements to PMU 920 which are applicable to all kinds of gates and circuit variations in dual VCC voltage circuitry for multiple-supply-voltage applications. Also FIG. 66 shows an example circuit useful in providing a three-state (floating) operation, thanks to the enabling/disabling transistors 6612, 6642, as for a data bus connection at OUT on the higher VCC side of the boundary. Power Management Unit (PMU) In Fig. 23, PMU State Definitions are as follows: In the READY state, the system is fully powered up and runs at full speed. Individual devices may be powered down. The STANDBY state conserves power by adjusting CPU turn-on time by a Mask Clock circuit of Fig. 27. The TEMPORARY state is similar to the READY state, and is entered through the STANDBY state (by a system event, a KBC or mouse interrupt). After a short-duration timer times out, the system will return to the STANDBY state. The 3-V SUSPEND state differs from the T(off) duration of the STANDBY state in the following respects: All the clocks, not just the CPU clock, are stopped. The MPU crystal oscillating circuitry is disabled. All the peripheral devices can be powered down, without regard to status of the peripheral timers. A resume from 3-V SUSPEND can be caused by either RTC alarm, modem ring, keyboard or mouse interrupts, suspend/resume button, on/off button, CRDSMI from PCU112, or a low-to-high transition on the BATLOW signal. The 0-V SUSPEND state has the lowest level of power consumption available. System state is stored to disk by software. All components, except the RTC 918 and the resume logic of the PMU, are powered down. The system can resume by Fig. 21 SRBTN input, ONBTN input, or RTC alarm. The OFF state is the same as 0-V SUSPEND except the system state is not stored to disk and the SRBTN input will not turn the system on. The state transitions A,B, ,,,Q,R for Fig. 23 are explained in the next table. The Fig. 23 state machine control logic 2035 is defined by the logic in chis table which is straightforwardly implemented as electronic logic from the logic information in the table. Conjunctions "and" and "or" refer to Boolean AND and OR. Parentheses (), brackets [] and braces () group Boolen expressions. State Transition Table for Fig. 23 Path Transition Software/Hardware State A READY --> STANDBY [Software writes the STATE bits of the PMU_CNTRL register (base address: 0A0h-0A2h) with 01] B READY --> 3-V SUSPEND [Software writes the STATE bits of the PMU_CNTRL register (base address: 0A0h-0A2h) with 10] and (SUSPSEL bit is 1) C READY --> 0-V SUSPEND [Software writes the STATE bits of the PMU_CNTRL register (base address: 0A0h-0A2h) with 10] and (SUSPSEL bit is 0 D READY --> OFF [Software writes the STATE bits of the PMU_CNTRL register (base address: 0A0h-0A2h) with 11] or [(PWRGD3) input transits from high to low) and (BATLOW input is active)] E STANDBY --> READY [Software writes the STATE bits of the PMU_CNTRL register (base address: 0A0h-0A2h) with 00] or (STANDBY timer doesn't time out) F STANDBY --> TEMPORARY (STANDBY timer times out but TEMPORARY timer doesn't time out) G STANDBY --> 3-V SUSPEND [Software writes the STATE bits of the PMU_CNTRL register (base address: 0A0h-0A2 with 10] and (SUSPSEL bit is 1) H STANDBY --> 0-V SUSPEND [Software writes the STATE bits of the PMU_CNTRL register (base address: 0A0h-0A2h) with 10] and (SUSPSEL bit is 0) I STANDBY --> OFF [Software writes the STATE bits of the PMU_CNTRL register (base address: 0A0h-0A2h) with 11] or [(PWRGD3 input transits from high to low) and (BATLOW input is active)] J TEMPORARY --> READY [Software writes the STATE bits of the PMU_CNTRL register (base address: 0A0h-0A2h) with 00] or (STANDBY timer doesn't time out) K TEMPORARY --> STANDBY (Both STANDBY and TEMPORARY timers time out) L TEMPORARY --> 3-V SUSPEND [Software writes the STATE bits of the PMU_CNTRL register (base address: 0A0h-0A2h) with 10] and (SUSPSEL bit is 1) M TEMPORARY --> 0-V SUSPEND [Software writes the STATE bits of the PMU_CNTRL register (base address: 0A0h-0A2h) with 10] and (SUSPSEL bit is 0) N TEMPORARY --> OFF [Software writes the STATE bits of the PMU_CNTRL register (base address: 0A0h-0A2h) with 11] or [(PWRGD3 input transits from high to low) and (BATLOW input is active)] O 3-V SUSPEND --> READY [(INBLRES bit is 0) or (BATLOW input is inactive)] and [(S/R Button is pushed) or [(On/Off Button is pushed) and (RMSKOBTN bit is 0)] or [(Alarm input is high) and (RMSKALARM bit is 0)] or [(Ring input is high) and (RMSKRING bit is 0)] or [(PCMCIA generates an CRDSMI) and (RMSKCRDSMI bit is 0)] or [(Keyboard or mouse interrupts) and (RMSKFBMS bit is 0) or [(BATLOW input transits from low to high) and (BLRES bit is 1)]} P 3-V SUSPEND --> OFF (PWRGD3 input transits from high to low) and (BATLOW input is active) Q 0-V SUSPEND --> READY [(INBLRES bit is 0) or (BATLOW input is inactive)] and (S/R Button is pushed) or [(On/Off Button is pushed) and (RMSKOBTN bit is 0)] R OFF --> READY [(On/Off Button is pushed) and (BATLOW input is inactive)] Power State Information for each PHU state of Fig. 23 Power-Up Status Ready Standby Temporary 3-V Suspend 0-V Suspend off VCC to MPU on on On on off Off VCC to PCU On on On on Off Off VCC to PPU (less PMU) On On On On Off Off VCC to KBC On On On On off Off VCC to DRAM On On On On Off Off VCC to PMU Other Logic On On On On Off Off VCC to PMU Resume Logic On On On On On On VCC to RTC On On On On On on VCC to Peripherals Dynamic Dynamic Dynamic Off Off System Data and Status Active Active Active Stored in DRAM Stored on disk Not saved Peripheral Timers Active Active Active Active Stopped Cleared Stopped Cleared CPU Clock On T(on)/T(of f) on Off Off Off Other Clocks Active Active Active Off Off Off Exit From This State A to D E to I J to N O, P Q R When the system is in the READY or TEMPORARY states, the HISPD input of Fig. 27 is high and MASKCLK is always inactive (high). When the system is in the 3.3-V SUSPEND, 0-V SUSPEND or OFF states MASKCLK is always active (low). When the system is in the STANDBY state MASKCLK is modulated as in Fig. 27 between two adjacent system timer interrupts (IRQ0's) or two adjacent periodic SMI's. This signal is inactive for a fraction of time then becomes active for the rest of the period. The inactive/active (Ton/Toff) ratio is determined by the TONTOFF register 2510. In addition, if a keyboard interrupt, a mouse interrupt, a PCI bus master request, or (optionally) a system event occurs, the MASKCLK becomes inactive for a period of time, which is determined by the Temporary Timer TEMP programming bits 20-23 of the PMU_TIMER register. Turning now to the subject of clocks, and referring to Fig. 37, all PPU clock signals are derived from four primary clock signals. These primary clocks are: PCLK. This is the PCI clock signal as specified in the PCI Revision 2.0 Specification. 14MHZ_CLK. 14.31818-MHz clock signal is generated by PPU on-chip oscillator and external crystal. 32KHZ_CLK. 32.768-kHz clock signal is generated by PPU on-chip RTC oscillator and external crystal. 48MHZ_CLK. 48-MHz clock signal is generated by PPU on-chip oscillator and external crystal. The 32kHz_CLK is powered by RTCPWR and is always active. The other primary clocks are active during Power-On-Reset, but stopped during SUSPEND. When a resume event occurs, clock stable indications from the PMU are used to produce stabilized versions of the primary clocks. All secondary clocks are derived from the three stabilized versions of the primary clocks, that is they are active during reset and inactive during suspend and for a predetermined time after a resume event. The next table shows the various internal PPU clocks and their derivation. Clock Signal Nominal Value(s) Used by Derivacion SYSCLK 16, 12, or 8 MHz Fast-AT Bus and DMA controller PCLK/2, /3, or /4 FDCCLK 24 MHz FDC 48 MHZ_CLK/2 KBCCLK 16, 12, 8 or 4 MHz KBC (external) 48 MHZ_CLK/3, /4, /6, /12 SIFCLK0 1.8461 or 8 MHz Serial Port 0 48 KHZ_CLK/26 or /6 PARCLK 8 MHz Parallel Port 48 MHZ_CLK/6 TMRCLK 1.193 MHz Timers 14 MHz_CLK/12 Secondary clocks are disabled when the corresponding Block Enable signal (from PCI-space configuration registers) is inactive. Secondary clock frequency switching and enabling/disabling is performed with circuits that prevent glitches. Each clock divider is provided with a short reset by the PMU after power up and 0-V resume. SOURCE_SMI Register Base Address = 0A8h-0AAh Bits in this register indicate which event triggered the SMI. These bits can be cleared by a write to this register, or set by power management software of Fig. 46. Bit Name Access Description 23 SWSMIR R This bit indicates that an SMI is generated by software. 22 - 21 TRPIDE R An IDE I/O is trapped. 20 TRPFDD R A FDD I/O is trapped. 19 TRPCOM1 R A serial port ( COM1 ) I/O is trapped. 18 TRPLPT1 R A parallel port ( LPT1 ) I/C is trapped. 17 TRPPCS0 R A programmable chip select ( PCS0 ) is trapped. 16 TRPPCS1 R A programmable chip select ( PC31 ) is trapped. 15 BATLOW R An SMI is generated by a high-to-low transition on the BATLOW input which will set this bit. 14 ONOFFBTN R This bit indicates that an SMI is generated by the ONBTN input. 13 SUSPBTN R This bit indicates that an SMI is generated by the SRBTN input. 12 GPSMI R This bit indicates that an SMI is generated on the GPSMI pin. 11 CRDSMI R This bit indicates that an SMI is generated on the PCMCIASMI CRDSMI. 10 PERIODICSMI R This bit indicates that a periodic SMI is generated in the STANDBY state. 9-7 - 6 STDBYTO R An SMI is generated by the STANDBY timer timed out. 5 SUSPTO R An SMI is generated by the SUSPEND timer timed out. 4 VGATO R An SMI is generated by the VGA timer timed out. 3 IDETO R An SMI is generated by the IDE timer timed out. 2 FDDTO R An SMI is generated by the FDD timer timed out. 1 SIUTO R An SMI is generated by the Serial/Parallel timer timed out. 0 PCSTO R An SMI is generated by the programmable chip select (s) timer timed out. MASK_SMI Register Base Address = 0ACh-0AEh Bit Name Access Description 23 SWSMIW W A write to this bit will generate an SMI. 22 - 21 MSKTRPIDE R/W Mask the SMI generated by the IDE I/O trap. 20 MSKTRPFDD R/W Mask the SMI generated by the FDD I/O trap. 19 MSKTRPCOM1 R/W Mask the SMI generated by the COM1 I/O trap. 18 MSKTRPLPT1 R/W Mask the SMI generated by the LPT1 I/O trap. 17 MSKTRPPCSO R/W Mask the SMI generated by the PCS0 trap. 16 MSKTRPPCS1 R/W Mask the SMI generated by the PCS1 trap. 15 MSKBATLOW R/W Mask the SMI generated by the BATLOW input. 14 MSKONBTN R/W Mask the SMI generated by toggling the On/Off button. 13 MSKSUSPSTN R/W Mask the SMI generated by toggling the Suspend/Resume button. 12 MSKGPSMI R/W Mask the SMI generated by the GPSMI input pin. 11 MSKCRDSMI R/W Mask the SMI generated by the PCMCIASMI CRDSMI. 10 MSKPRDSMI R/W Mask the periodic SMI in the STANDBY state. When this bit is not set, a periodic SMI is generated and wakes up the system by enabling the MSKCLK output to CPU; if it is set to 1, the task is performed by System Timer 0, which generates an IRQ0 every 55ms. 9-8 SMIPRD1-0 R/W Set the time period between two successive periodic SMI's. SMIPRD1 SMIPRD0 Time Period 0 0 125 ms 0 1 250 ms 1 0 500 ms 1 1 1 second 7 - 6 MSKSTDBYTO R/W Mask the SMI generated by the STANDBY timer timed out. 5 MSKSUSPTO R/W Mask the SMI generated by the SUSPEND timer timed out. 4 MSKVGATO R/W Mask the SMI generated by the VGA timer timed out. 3 MSKIDETO R/W Mask the SMI generated by the IDE timer timed out. 2 MSKFDDTO R/W Mask the SMI generated by the FDD timer timed out. 1 MSKSIUTO R/W Mask the SMI generated by the SIU timer timed out. 0 MSKPCSTO R/W Mask the SMI generated by the programmable chip-select timer timed out. MASK_SYSTEM Register Base Address = 0B0h-0B3h Bits in this register are used to mask system events which are not intended to be monitored by the STANDBY and the SUSPEND timers. When a bit is set to 1 that particular event will be masked. Bit Name Access Description 31-30 - 29 STDBYPCI R/W Mask PCI events (form the DEVSEL input) off the STANDBY timer event monitoring. 28 STDBYCSI R/W Mask PCMCIA card service interrupts off the STANDBY timer event monitoring. 27 STDBYVGA R/W Mask VGA events (from VGA Chip select) off the STANDBY timer event monitoring. 26 STDBYDMA R/W Mask DMA requests off the STANDBY timer event monitoring 25 STDBYIDE R/W Mask IDE events off the STANDBY timer event monitoring. 24 STDBYFDD R/W Mask FDD events off the STANDBY timer event monitoring. 23 STDBYPCSO R/W Mask the first programmable chip select ( PCS0 ) events cff the STANDBY timer event monitoring. 22 STDBYPCS1 R/W Mask the second programmable chip select ( PCS1 ) events off the STANDBY timer event monitoring. 21 STDBYCOM1 R/W Mask COM1 events (COMICS + IRQ for COM1) off the STANDBY timer event monitoring. 20 STDBYLPT1 R/W Mask LPT1 events (LPT1CS + IRQ7) off the STANDBY timer event monitoring. 19 STDBYIRQ9 R/W Mask IRQ9 off the STANDBY timer event monitoring. 18 STDBYIRQ10 R/W Mask IRQ10 off the STANDBY timer event monitoring. 17 STDBYIRQ11 R/W Mask IRQ11 off the STANDBY timer event monitoring. 16 STDBYIRQ15 R/W Mask IRQ15 off the STANDBY timer event monitoring. 15 - 14 SUSPKBMS R/W Mask keyboard and mouse interrupts off the STANDBY timer event monitoring. 13 SUSPPCI R/W Mask PCI events off the STANDBY timer event monitoring. 12 SUSPCSI R/W Mask PCMCIA card service interrupts off the STANDBY timer event monitoring. 11 SUSPVGA R/W Mask VGA events off the STANDBY timer event monitoring. 10 SUSPDMA R/W Mask DMA requests off the STANDBY timer event monitoring. 9 SUSPIDE R/W Mask IDE events off the STANDBY timer event monitoring. 8 SUSPFDD R/W Mask FDD events off the STANDBY timer event monitoring. 7 SUSPPCSO R/W Mask the first programmable chip selece ( PCS0 ) events off the STANDBY timer event monitoring. 6 SUSPPCS1 R/W Mask the second programmable chip select ( PCS1 ) events off the STANDBY timer event monitoring. 5 SUSPCOM1 R/W Mask the serial port ( COM1 ) events off the STANDBY timer event monitoring, 4 SUSPLPT1 R/W Mask the parallel port ( LPT1 ) events off the STANDBY timer event monitoring. 3 SUSPIRQ9 R/W Mask IRQ9 off the STANDBY timer event monitoring. 2 SUSPIRQ10 R/W Mask IRQ10 off the STANDBY timer event monitoring. 1 SUSPIRQ11 R/W Mask IRQ11 off the STANDBY timer event monitoring. 0 SUSPIRQ15 R/W Mask IRQ15 off the STANDBY timer event monitoring. MASK_SIU_VGA Register Base Address = 0B4h Bit Name Access Description 7-6 - 5 MASKPCOM1 R/W When the bit is set, COM1 chip select and interrupt events will not affect the SIU power control output. 4 MASKPLPT1 R/W When the bit is set, LPT1 chip select and interrupt events will not affect the SIU power control output. 3-2 - 1 MASKPKBMS R/W When the bit is set, keyboard and mouse interrupt events will not affect the graphics (VGA frame buffer) idle timer. 0 MASKPVGA R/W When the bit is set, VGA frame buffer access events will not affect the graphics idle timer. SW_PWR_CNTL Register Base Address = 0B8h Bits in the register will let the software, instead of the hardware, control the power to peripheral devices. When the odd-number bits in this register are reset to 0 (return control to hardware), the corresponding hardware timer will also be reset. Bit Name Access Description 7 SWCNTLIDE R/W Software control the IDE power output. 6 SWIDEPWR R/W 1 = Turn on the IDE power output. 0 = Turn off the IDE power output. 5 SWCNTLFDD R/W Software control the FDD power output. 4 SWFDDPWR R/W 1 = Turn on the FDD power output. 0 = Turn off the FDD power output. 3 SWCNTLSIU R/W Software control the SIU power output. 2 SWSIUPWR R/W 1 = Turn on the SIU power output. 0 = Turn off the SIU power output. 1 SWCNTLPCS R/W Software control the programmable chip-select power output. 0 SWPCSPWR R/W 1 = Turn on the programmable chip-select power output. 0 = Turn off the programmable chip-select power output.

Claims: A digital system (100) comprising a processor (102) connected to receive a clock signal with a clock gate (2540) for selectively enabling the clock signal to operate the processor, and a control circuit controllably connected to the clock gate, characterized in that the control circuit comprises: a first logic circuit (708) responsive to a software controllable enabling input (REGCON6) to provide a clock control signal (SUSPX) in a first state to disable the clock gate when the software controllable enabling input is in a first state, with at least one interrupt input (HNMI, HINTR), wherein the first logic circuit is operable to provide the clock control signal in a second state to enable the clock gate in response to the at least one interrupt input when the software controllable enabling input is in the first state; and a second logic circuit (2340) coupled to the first logic circuit by a modulation signal(MASKCLK), the second logic circuit having a software controllable register (2510), the second logic circuit operable to modulate the clock control signal in a periodic manner with a selectable duty cycle responsive to the software controllable register. The digital system of Claim 1, wherein the first logic circuit further comprises a suspend input (HSUSPENDX), the first logic circuit responsive to the suspend input to place the gate control signal in the first second state to disable the clock gate and to supply a stop signal (HSTOPTOMMCU) to a memory controller (718), and further responsive to a stop acknowledge input (HSTOPFMCU) from said memory controller to supply a stop oscillator signal (STOPOSC, HSTOPOSC, 706) to stop at least one clock circuit. The digital system according to claim 2, wherein: the first circuitry further comprises a resume input (HRESUME), the first circuit operable to place the clock control signal in the first state to disable the clock gate in response to removing the resume input, a portion of the first logic circuit (2830) is responsive to changes in the suspend input (HSUSPENDX) to remove the stop oscillator signal thereby allowing generation of the clock signal; and the clock circuit is operable to start in response to removing the stop oscillator signal and to supply the resume signal after a predetermined number of cycles of said clock signal have occurred. The digital system of any preceding claim, wherein the second logic circuit is operable to override the first logic circuit such that the gate control signal is modulated even if the software controllable input is in the first state. The digital system according to any preceding Claim, wherein the second logic circuit further comprises: a counter (2520) with a clock input; comparison circuitry (2530) connected to the counter and to the software controllable register, the comparison circuitry having a modulation signal output (MASKCLK) connected to the first logic circuit, the comparison circuitry operable to provide the modulation signal in a manner that the period is determined by the counter and the duty cycle is determined by a value stored in the software controllable register. The digital system according to Claim 5, further comprising clock selection circuitry (2562, 2570, 2572) connected to the clock input operable to select from a plurality of clocks, whereby the period of the modulation signal is varied. The digital system according to Claim 6, further comprising gating circuitry (2535) connected to the modulating signal, the gating circuitry having one or more control inputs operable to disable the modulation signal. The digital system according to any previous Claim, further comprising a printed wiring board (302) having a substantially insulative planar board element, conductors in or on said board element; a first integrated circuit (102) mounted on said printed wiring board; a second integrated circuit (110), mounted on said printed wiring board and coupled to said first integrated circuit via said conductors, and wherein the first circuit is contained within the first integrated circuit and the second circuit is contained within the second integrated circuit. A method of operating a digital system, comprising the steps of: generating a system clock signal for clocking a processing unit; selectively gating the clock signal so that the processing unit operates at different speeds in order to conserve power; characterized in that the step of selectively gating comprises: suspending clock operation by invoking the clock signal gate in response to a software command to place the system in a low power standby mode; responding to an interrupt by removing the clock signal gate so that the system resumes operation; and modulating the clock signal gate to operate the system in a reduced power mode. The method of Claim 9, wherein the step of modulating comprises the steps of: providing a mask signal (MASKCLK) having a period, wherein the period is large compared to the system clock signal; selecting a duty cycle by writing a duty cycle value to a register (2510) under software control; invoking the clock signal gate while the mask signal is in a first state in response to the duty cycle value; and removing the clock signal gate while the mask signal is in a second state in response to the duty cycle value, whereby the system periodically operates at full speed while the mask signal is in the first state and ceases operating while the mask signal is in the second state. The method of Claim 10, further comprising the step of selecting the period of the mask signal by selecting from a plurality of clock signals under software control; and wherein the step of providing the mask signal determines the period by dividing the selected clock signal by a given amount.

Inventors: CHEN IAN, JOE JOSEPH, TAKAHASHI YUTAKA, WALSH JAMES J, CHEN, IAN, JOE, JOSEPH, TAKAHASHI, YUTAKA, WALSH, JAMES J.
Applicants: TEXAS INSTRUMENTS INC, TEXAS INSTRUMENTS INCORPORATED
Application year: 1995
Main classification: G06F1
IPC codes: G06F3, G06F1, G06F9