Abstract:
Each modular processor card of a modular electronic system carries a component defining its maximum current or power requirements. The component, which may be a resistor, capacitor, serial access memory, or the like, is accessible over a single conductor through a backplane by a power supervisor. The supervisor will determine the current/power requirements of a processor card while the card is substantially powered off. The supervisor may then weigh existing power supply resources of the modular electronic system with existing current/power demand and make a decision to allow power-up of the card if sufficient overhead is available, or, alternatively, make a decision to deny power-up of the card if insufficient additional current/power resources are available. An optional message indicating the outcome of the decision can be transmitted to a user. If the supervisor elects to power up the card, a signal sent on the conductor connecting the card to the supervisor may be used to authorize the card to power up and control circuitry to effect the power up.

Description:
This application is a continuation of Ser. No. 09/041,838 filed Mar. 12, 1998 U.S. Pat. No. 6,134,666. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention is directed to a method and apparatus which permit a power supervisor in a multi-card modular electronic system to turn on or off power to a given modular processor card based upon considerations of the power needed by the card and the power resources available to the modular electronic system. 
     2. The Background Art 
     Multi-card modular electronic systems are common in the computer industry. Typically such systems comprise a back plane having a plurality of connectors to which a number of line cards or processor cards are connected. Processor cards may perform any of a number of functions as well known to those of ordinary skill in the art. The back plane provides electrical interconnections to the processor cards, such as data, power, ground and signalling. Such systems usually include at least one supervisor module which may be on one of the processor cards or may be permanently connected to the back plane. Supervisor modules are commonly used to detect errors and report conditions to a user. 
     It is desirable to build modular systems which provide for future expansion while providing a relatively low entry cost. In systems employing processor cards which consume significant quantities of power, such as those embodying one or more microprocessors, or equivalently power hungry devices, it may be desirable to provide for modular power supplies which may be added or changed as power requirements increase with the addition of is more processor cards or the substitution of higher power consumption processor cards for lower power consumption processor cards. 
     In such systems, it is frequently a problem that an individual responsible for such systems may inadvertently place too high a power demand upon a particular power supply configuration of such a system through the addition of a particular processor card to a previously functioning system. The consequences can vary from a simple shut down or an inability to start up to equipment damage. Accordingly, it would be desirable to provide a method and apparatus which could simply protect such systems from the consequences of errors made by inadvertently overlooking available power supply resources in such modular electronic systems. 
     As back plane conductor lines are a relatively scarce and expensive resource in such systems, it would also be desirable to implement such method and apparatus in a manner which makes a minimum use of such scarce resources. 
     SUMMARY OF THE INVENTION 
     Each modular processor card of a modular electronic system carries a component defining its maximum current or power requirements. The component, which may be a resistor, capacitor, serial access memory, or the like, is accessible over a single conductor through a backplane by a power supervisor. The supervisor will determine the current/power requirements of a processor card while the card is substantially powered off. The supervisor may then weigh existing power supply resources of the modular electronic system with existing current/power demand and make a decision to allow power-up of the card if sufficient overhead is available, or, alternatively, make a decision to deny power-up of the card if insufficient additional current/power resources are available. An optional message indicating the outcome of the decision can be transmitted to a user. If the supervisor elects to power up the card, a signal sent on the conductor connecting the card to the supervisor may be used to authorize the card to power up and control circuitry to effect the power up. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an electrical schematic diagram of a presently preferred embodiment of the present invention. 
     FIG. 2 is an electrical schematic diagram of a typical power soft start circuit for use in conjunction with a presently preferred embodiment of the present invention. 
     FIG. 3 is a system block diagram of an alternative preferred embodiment of the present invention. 
     FIG. 4 is a system block diagram of another alternative preferred embodiment of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Those of ordinary skill in the art will realize that the following description of the present invention is illustrative only and is not intended to be in any way limiting. Other embodiments of the invention will readily suggest themselves to such skilled persons from an examination of the within disclosure. 
     Turning to FIG. 1, a presently preferred embodiment of the present invention is shown. In accordance with the present invention, a modular electronic system  10 , such as computer communications equipment, has a backplane connector strip  12  which provides electrical interconnections among a plurality of electronic modules or cards which are electrically attached to it (e.g., plugged into it). The invention will work with one or more electronic modules. 
     In such modular electronic systems, one or more power supplies may be provided having certain power or current delivery capabilities. To render such systems more flexible, a plurality of positions can be provided into which such power supplies may be installed. The problem is that given a very flexible level of power supply resources and a very flexible level of power demand posed by the electronic modules which may be attached to the backplane, the modular electronic system now must monitor both its resources and its power demand to insure that there is no shortfall of power which might cause system unreliability or failure. 
     In accordance with a presently preferred embodiment of the present invention, a power supervisor  14  is provided. The power supervisor  14  has a communications link  16  to one or more power supplies  18 ,  20 ,  22  which communicates information defining available power resources to a microprocessor  24  of power supervisor  14 . This communication may be carried out in any of a number of ways. 
     According to a presently preferred embodiment of the present invention, each power supply module  18 ,  20 ,  22  may have stored in it a relatively permanent memory having a three (or more) bit identification code that can be read by power supervisor is  14  over communications link  16 . Each power supply  18 ,  20 ,  22  will have its proper predefined identification code set at the time of its manufacture to a value unique for its model and/or indicative of its maximum ability to supply power or current. In typical use the power supervisor  14  will read the identification code at power up,, and/or at any time that the power supply module  18 ,  20 ,  22  is inserted into or attached to power supervisor  14 . Power supervisor  14  then takes the identification code for the power supply module, and if necessary, looks up in a table associated with power supervisor  14  the identification code in order to determine a power output value for the power supply. 
     In an alternative preferred embodiment, in order to provide more information without relying on software tables embedded in power supervisor  14 , a serial EEPROM is used in each power supply module  18 ,  20 ,  22 . The serial EEPROM is preferably programmed at the time of manufacture of the power supply module with information apropos of the power supply module, e.g., output voltages, input voltages, current levels, operating characteristics, model, type, serial number, manufacturer, and the like. This information is then read at power up, or at insertion or attachment of the power supply module to power supervisor  14  so that power supervisor  14  is fully advised of the operating characteristics of the power supply modules attached to it and can act on that information. A benefit of this latter approach is that new power supply modules can be created after power supervisor  14  is fixed and installed and power supervisor  14  can still make full use of the information encoded in the serial EEPROM without any need for an upgrade or software update to the power supervisor. Other non-volatile memory devices could also be used instead of the serial EEPROM discussed above, as would be understood by those of ordinary skill in the art. Preferably such devices would use a single bit data path in order to minimize connections between power supervisor  14  and power supply modules  18 ,  20 ,  22 . 
     Electronic module  26  attaches to backplane  12 . Each electronic module will have a particular power requirement. Obviously the power demand of module  26  will fluctuate depending upon what it is doing at a particular moment, but it will have a known maximum power requirement or demand which can be thought of as the worst case power requirement. It is this known maximum power requirement that must be communicated to power supervisor  14 . 
     In accordance with a presently preferred embodiment of the present invention, the maximum power requirement is communicated by an analog voltage signal on a query conductor  28  passing from electronic module  26  through backplane  12  to power supervisor  14 . Query conductor  28  is connected to a first source of a voltage, such as Vcc  30  through resistor R 1  which may be a 100 ohm resistor. Analog to digital converter  32  converts the voltage on query conductor  28  to a digital value for use by programmed microprocessor  24 . A component, such as an impedance element, which may be a resistor, Rset  34 , disposed between query conductor and a source of a second voltage  36 , such as ground, encodes a voltage signal on query conductor  28 , the voltage being a function of the resistance of resistor  34 . For example, Rset  34  could be 25 ohms if power demand of the module is 5 amperes, 50 ohms if 10 amperes, 75 ohms if 15 amperes, and 100 ohms if 20 amperes. 
     The voltage drop between Vcc  30  and query line  28  through R 1  is selected to be sufficient to prevent current flow through zener diode D 1 , thus isolating the portion of the circuitry of module  26  connected to the anode  38  of zener diode from query line  28 . 
     If microprocessor  24  decides that sufficient power resources are available to permit module  26  to be turned on with its now known maximum power requirement, then microprocessor  24  sends a signal “PWRUP” on line  40  to a switch shown here as transistor Q 1 . The presence of the PWRUP signal on the control gate of transistor Q 1  permits current to flow through Q 1  from Vcc to query line  28 . This voltage, not dropping through resistor R 1 , will cause a higher voltage to obtain on query line  28 . This voltage will be selected to be above the threshold of zener diode D 1 . In turn, current will flow through resistors R 2  and R 3  providing a signal on a control gate of transistor Q 2  which assumes the role of a switch. When this current flows, Q 2  will turn on and provide an ENABLE signal on line  42  to power circuit soft start  44 . 
     Power circuit soft start  44  operates in a conventional manner, such as that shown in FIG. 2, to slowly turn on power available on line  46  and apply it to the power consuming circuitry of module  26  denoted “A” while the ENABLE signal is asserted on line  42 . Note that “A” will be provided with a slightly lower voltage “V” than Vcc (V+e) available at backplane  12  due to the voltage drop (e) through transistor Q 3  which is preferably a power MOSFET. C 1  is preferably 0.1 uF and C 2  and C 3  are filter capacitors chosen based upon the application. The circuit shown in FIG. 2 is for reference only. An actual implementation would likely contain additional components needed to control the power slope as known to those of ordinary skill in the art. 
     Those of ordinary skill in the art will realize that other components may be used to encode the maximum power demand of module  26  on query conductor  28 . For example, capacitors, power supplies, and other elements having unique electrical characteristics capable of being read remotely over a single conductor could be used. Turning to FIGS. 3 and 4, a more sophisticated implementation of the present invention is shown. In FIG. 3 the component is a communications register  48 . Power supervisor  50  communicates with communications register  48  over query line  52  which passes through backplane  54 . Module  56  also communicates with communications register  48  over line  58 . Power supervisor  52  may send messages to module  56  via communications register  48  which is preferably a one-bit wide data communications path. Communications register  48  is preferably a serial register or serial access memory device or the like. Communications from power supervisor  50  to module  56  may include, for example, messages along the lines of “send your maximum power requirement”, “send your model type” (so that the power supervisor could determine from its pre-programmed memory what the maximum power demand is), “go ahead and start up”, “do not start—maximum power exceeded”, and the like. Power may be provided to register  48  and module  56  during this pre-start period via line  60  connected to Vcc  62  through backplane  54  as these devices typically require some minimal amount of power in order to function. This minimal power, however, is negligible relative to the full maximum power requirement of the module  56 . 
     A soft-start circuit along the lines of FIG. 2 (or equivalent) would preferably be incorporated into Module  56 . If a “go ahead and start up” signal is received by module  56 , the soft-start circuit would be activated to bring the module on line. 
     FIG. 4 shows a refinement of the embodiment of FIG.  3 . In FIG. 4, power supervisor  64  communicates with module  66  over a query line  68  which passes through backplane  70 . Module  66  is provided with a prestart area  72 . Prestart area  72  is provided with power over line  74  from a backplane connection to Vcc  76 . Prestart area  72 &#39;s circuitry is powered by connection to line  74 , but the bulk of the power-consuming circuitry of module  66  remains unpowered until the prestart area  72  receives instructions from power supervisor  64  to turn on module  66 . The prestart area  72  may carry on extensive communications with power supervisor  64  and power supervisor  64  may require information in addition to maximum power requirement—for example, a password could be required, or a particular range of serial numbers could be required. The power supervisor  64  could be programmed to disallow the power up of unauthorized devices or devices known to be incompatible with the particular modular electronic system in question. Some of these functions could also be included in the FIG. 3 embodiment. 
     In accordance with the various preferred embodiments of present invention the connections to a plurality of modules could be carried out with a plurality of query lines, each with a connection to the power supervisor, or with a single conductor connection to the power supervisor multiplexed to the plurality of modules in a conventional manner. 
     It is intended that the system provided herein would be capable of “hot swapping” of module cards and/or power supply modules. In this manner, the system would be operating and an additional card would be plugged into a slot on the backplane. The power supervisor would detect the insertion of the card in a conventional manner and would query the module to determine if turning it on would exceed power resources available to the system. The system could also work without a “hot swapping” capability. 
     The term “power” has been used herein but is meant to include current level at a particular voltage, a combined power demand comprising a multiple voltage power demand at various currents, and the like, depending upon the system characteristics. For example, if all power used by the module is at 3.3 V, then the only variable is current. However, if the module uses 3.3 V power as well as 5 V power, those of ordinary skill in the art will readily see how the system described above could easily be expanded to cover a multi-voltage system. While a multiplexing scheme, for example, could be used to scan for a number of different voltage requirements, or different voltage/current combinations could be encoded with a single component, multiple query conductors could also be used, if more convenient. 
     The power supervisor may itself be a module plugged into the backplane, or it may assume another physical embodiment, as long as it has the required connections to the backplane conductors. 
     Alternative Embodiments 
     Although illustrative presently preferred embodiments and applications of this invention are shown and described herein, many variations and modifications are possible which remain within the concept, scope, and spirit of the invention, and these variations would become clear to those of skill in the art after perusal of this application. The invention, therefore, is not to be limited except in the spirit of the appended claims.