Electronic system having a microprocessor and a coprocessor disposed on a circuit mounting board

Abstract: An electronic system has a first (24) and a second semiconductor device (25) acting as a microprocessor and a coprocessor, respectively, disposed linearly on a mounting board (20). The external pins (24D, 25D) of the first and the second semiconductor device (24,25) are connected by wiring means installed linearly on the mounting board.

Description: The present invention relates to a semiconductor device and an electronic system having a plurality thereof disposed on a mounting board. There have been developed CPU boards each having a microprocessor (CPU) and its coprocessors mounted thereon to form an electronic system. An example of such coprocessors is a floating point unit. The semiconductor chips that include the microprocessor and coprocessors mentioned above are usually accommodated in a pin grid array (PGA) each. A semiconductor device of a PGA construction may have between tens and hundreds of external pins disposed around its periphery. In other words, the semiconductor device of the PGA construction is suitable for accommodating a semiconductor chip such as a microprocessor or a coprocessor dealing with numerous signals. Electronic systems of this kind incorporating microprocessors and coprocessors are illustratively found in pp. 123-138 of "Nikkei Electronics," of the July 13, 1987 issue. The microprocessor and coprocessors to be mounted on the board of an electronic system such as those cited above are each designed and developed separately. That is, the arrangement of external pins of semiconductor devices based on the PGA construction has not been standardized. For this reason, it has been impossible for the board of such microprocessors or coprocessors to dispose linearly, say, the conductors carrying clock or coprocessor signals between their corresponding external pins; these conductors must be installed over long distances and/or disposed so as to cross other signal conductors. This has led to increases in both capacity and resistance of the signal conductors, causing delays in signal transmission. Because a CPU and its coprocessors perform synchronized transfer between them, clock skews that may occur between the CPU and any of its coprocessors or between coprocessors can cause malfunction of the system and hamper high-speed operations thereof. In particular, because the clock and coprocessor signals are respectively the reference signal and the signal of the highest velocity in an electronic system, any delay in these signals necessarily reduces the overall performance of the entire system. Delays in the above-mentioned coprocessor signals or clock signals disrupt the timing of the operation by the electronic system. This can result in system malfunction of the electronic system and reduce the electrical reliability thereof. There has been no special consideration given to the arrangement of external pins of those semiconductor devices of the PGA construction which accommodate the above-described microprocessor and coprocessors. That is, the external pins that transmit the data bus and address bus signals over bus lines are arranged more or less randomly around the external pins for clock signals. When any of the data bus and address bus signals changes in signal level, the clock signals suffer from a noise by electromagnetic induction on the external pins for those signals. The noise distorts the waveform of the clock signals. Where the clock signals are of a low-frequency type, low levels of distortion in the clock signal waveform do not affect the performance in any appreciable manner. However, where a high-frequency signal is used in a system having a clock-synchronized bus, even very low levels of distortion in the clock signal waveform can trigger system malfunction. For example, in an electronic system that this inventor was developing, clock signals of as high as 40 MHz were adopted to implement higher operation speeds and more frequent bus cycle reiteration. Clock signals operating on such a high frequency to activate the microprocessor and its coprocessors involved led to frequent system malfunction. GB-A-2040499 discloses a method of manufacturing an electrical circuit layout, in which semicondcutor devices are mounted on a circuit board, so that the external pins of each device are located in rows and extending in one direction, and corresponding pins of different devices are connected by conductive lines extending in a column direction relative to the rows of pins. Therefore, according to the present invention, there is provided an electronic system having a microprocessor and a co-processor accommodated in pin grid arrays, disposed on a circuit mounting board having conductive lines formed thereon, wherein said microprocessor has a plurality of external pins located in a matrix pattern of rows and columns and connected to respective ones of said conductive lines, said external pins comprising first external pins carrying clock signals and coprocessor control signals; said co-processor is disposed adjacent said microprocessor and has a plurality of external pins connected to respective ones of said conductive lines and located in a matrix pattern of rows and columns that are parallel to said rows and columns, respectively, of said microprocessor, said external pins of said co-processor comprising second external pins carrying said clock signals and said coprocessor control signals, whereby said first and second external pins are arranged such that corresponding ones of said first and second external pins are connected by selected ones of said conductive lines running linearly in the column direction. The present invention may thus permit the operation speed of an electronic system having a microprocessor and its coprocessors mounted on a board to be increased. The present invention may also permit the incidence of malfunction in the system to be reduced and the electrical reliability improved. The basic principles of examples of the present invention will now be explained in more detail. In an electronic system having a first and a second semiconductor device mounted on a board as a microprocessor and its coprocessor, respectively, there are provided signal conductors which are substantially linear on that board. Either the signal conductors are connected to the external pins with clock signals assigned thereto of the first semiconductor device, or the signal conductors are connected to the external pins with coprocessor signals assigned thereto of the second semiconductor device. In the first and the second semiconductor device each having external pins arranged in a matrix of m rows by n columns, with the ℓ-th column for the first semiconductor device comprising external pins having clock or coprocessor signals assigned thereto, the corresponding external pins for the second semiconductor device fall on one of the (ℓ - 1)th column, ℓ-th column and (ℓ + 1)th column. On the same row and the same column of the first and the second semiconductor each, there are disposed external pins for clock or coprocessor signals. Of the external pins of the first and the second semiconductor device, those disposed close to the clock signal conductors mounted on the board are connected to a fixed potential. The external pins located around those for clock signals of the first and the second semiconductor device are also connected to a fixed potential. The first and the second semiconductor device are each formed of a rectangular semiconductor chip with a plurality of external pins surrounding the sides thereof. Of these external pins, those on one side of the semiconductor chip and/or those on the opposite side thereof are the external pins for dealing with clock or coprocessor signals. By use of the means and arrangements outlined above, it is possible to shorten the length of the signal conductors for clock or coprocessor signals disposed on the board, thereby reducing delays in signal transmission and improving the operation speed of the electronic system accordingly. Where the first and the second semiconductor device are mounted on the board, it is possible to locate the external pins for clock signals and those for coprocessor signals in a substantially linear manner. The surroundings of the external pins for clock signals are electromagnetically shielded by means of fixed potential connection. This reduces the amount of noise generated into clock signals when the data bus signal is switched in signal level. Lowered noise levels in turn translate into the prevention of system malfunction, improving the electrical reliability of the electronic system. The surroundings of the clock signal conductors on the board are electromagnetically shielded by means of fixed potential connection. This reduces the amount of noise generated into clock signals when the data bus signal is switched in signal level. Lowered noise levels again translate into the prevention of system malfunction and help improve the electrical reliability of the electronic system. What follows is a description of a preferred embodiment according to the present invention. Throughout the drawings attached to facilitate the understanding of the embodiment as it is described, like reference characters designate like or corresponding parts. Repetitive portions of the description are omitted on the understanding that they can be readily and clearly inferred in the context. In the drawings, Fig. 1 is a block schematic diagram of major components constituting an electronic system which is a preferred embodiment of the present invention; Fig. 2 is a block diagram of the electronic system; Fig. 3 is a perspective view of a semiconductor device incorporated in the electronic system; Fig. 4 is a cross-sectional view of the semiconductor device; Fig. 5 is a bottom view of the semiconductor device; Fig. 6 is a schematic showing the functions of the external pins which are disposed on a microprocessor and depicted in Fig. 4; Fig. 7 is a schematic showing the functions of the external pins which are disposed on a coprocessor and depicted in Fig. 4; Fig. 8 is a layout plan of a semiconductor chip mounted on the semiconductor device; and Figs. 9 and 10 are bottom views of several major semiconductor devices as they are mounted on the electronic system. Fig. 2 is a block diagram that outlines an electronic system which is a preferred embodiment of the present invention. Shown in this figure is a CPU board that accommodates the electronic system 20 incorporating floating-point units (FPU's). On a mounting surface 20D of the board, there are provided connectors 21 shown at top and bottom of the figure. The connectors 21 are capable of connecting the electronic system 20 to external equipment. Between the upper and lower connectors, the mounting surface 20D contains I/O driver circuits 22, a clock generator (CLK) 23, a microprocessor (CPU) 24, coprocessors (FPU1-FPU4) 25 through 28, a memory circuit 29, and a peripheral circuit 30. One I/O driver circuit is located close to one of the upper and lower connectors 21, and the other I/O driver circuit close to the other connector. Each I/O driver circuit 22 comprises a plurality of semiconductor devices each illustratively formed of a semiconductor chip sealed in a dial in-line package (DIP). The clock generator (CLK) 23 is located close to the upper I/O driver circuit 22. This generator is a circuit that generates clock signals (system clock signals) that define the timing at which the electronic system 20 operates. The memory circuit 29 is located in the middle of the mounting surface 20D of the electronic system 20. This circuit comprises a plurality of semiconductor devices (semiconductor memories) each illustratively formed of a semiconductor chip (DRAM, SRAM, etc.) sealed in a DIP. The peripheral circuit 30 is disposed between the memory circuit 29 and the lower I/O driver circuit 22. As with the I/O driver circuits 22 and memory circuit 28, the peripheral circuit 30 comprises a plurality of semiconductor devices each illustratively formed of a semiconductor chip sealed in a DIP. The microprocessor 24 and the coprocessors 25 through 29 are located between the memory circuit 29 and the upper I/O driver circuit 22 on the mounting surface 20D. In this embodiment, the electronic system 20 comprises one microprocessor 24 and four coprocessors 25 through 28. As depicted in Figs. 1 and 2, the microprocessor 24 and the coprocessors 25 through 28 are disposed crosswise in a substantially linear manner. As shown in Figs. 3 and 4, the microprocessor 24 and the coprocessor 25 are each formed of a semiconductor device that adopts a PGA construction. Specifically, the microprocessor 24 and the coprocessor 25 are each made up of a semiconductor chip 24B (25B) placed in a cavity substantially in the middle of a base board 24A (25A) and sealed with a sealing cap 24C (25C). The semiconductor chip 24B (25B) is illustratively formed of a plane, monocrystal silicon substrate in rectangular shape. The base board 24A (25A) is illustratively formed of a plane ceramic board in substantially square shape (a rectangular shape is also possible). The base board 24A (25A) is not restricted to ceramic in terms of material; the board may also be formed of a plastic material. Because the cavity is provided on the face of the base board 24A (25A), the semiconductor chip 24B (25B) is located on the component side thereof. As shown in Figs. 3, 4 and 5, the back (mounting side) of the base board 24A (25A) has a plurality of external pins 24D (25D). These pins project perpendicularly from the back of the base board 24A (25A). As depicted in Fig. 5, the external pins 24D (25D) are disposed regularly along the four sides of the semiconductor chip 24B (25B). More specifically, the external pins 24D (25D) are arranged in a matrix of m rows by n columns on the back of the base board 24A (25A). In the middle of the base board is an area reserved to accommodate a semiconductor chip. There are no external pins in this area. The microprocessor 24 and the coprocessor 25 of this embodiment each contain a semiconductor device of the PGA construction in a matrix of 14 rows by 14 columns having, but not limited to, 135 external pins 24D (25D). The functions of the external pins 24D (25D) in Fig. 5 for the microprocessor and those for the coprocessor are shown in Figs. 6 and 7, respectively. Of the rows A through P (14 rows) shown in Figs. 6 and 7, any row crossing any of the columns shown points to the function that corresponds to that of the external pin 24D (25D) in the corresponding location in Fig. 5. In the case of the microprocessor in Fig. 6, the external pins 24D to the right of the semiconductor chip 24B are each assigned such signals as a reference potential Vss (GND), a power supply potential Vcc and coprocessor signals. Which signals correspond to which coprocessor signals will be described later. The external pins 24D to the left of the semiconductor chip 24B are each assigned such signals as a reference potential Vss, a power supply potential Vcc and clock signals CLKf and CLK2f. The external pins 24D on the top and bottom sides of the semiconductor chip 24B are assigned a data bus signal D0-D31 and an address bus signal A0-A29. The signal pins provide the following functions: 1. A0-29 (pins A2-A29) [Output (tri-state): address bus] Output a 32-bit address bus signal. This signal indicates an address during a data transfer cycle, an interruption level during an interruption acknowledge cycle, and a coprocessor ID number during coprocessor instruction transfer. 2. BC0-3 [Output (tri-state): bus control] Output a byte control signal. This signal indicates the location of effective byte data on the data bus. 3. D0-31 [Input/output (tri-state): data bus] Input and output a 32-bit data bus signal. 4. AS [Output (tri-state): bus control] Outputs an address strobe signal. This signal indicates that an effective address has been output onto the address bus. 5. BS [Output: bus control] Outputs a bus cycle start signal which indicates the start of a bus cycle. The signal lasts for one machine cycle. 6. DS [Output (tri-state): bus control] Outputs a data strobe signal indicating that there is effective data on the data bus. 7. R/ W [Output (tri-state): bus control] Outputs a read/write data signal that indicates the direction of data transfer. 8. DC [Input: bus control] Inputs a data transfer complete signal given by an external device. In a data read operation, the signal indicates that the external device has placed effective data was on the bus. In a data write operation, the signal indicates that the external device has received data. 9. ASCD [Input: bus control] Inputs an asynchronous data transfer complete signal given by an external device. In a data read operation, the signal indicates that the external device has placed effective data on the bus. In a data write operation, the signal indicates that the external device has received data. This asynchronous signal is not to be used where FPU's are utilized. 10. RNG [Output: bus control] Outputs a ring signal, which is a static signal. The MSB (corresponding to ring levels 0 and 1) in the RNG field of the PSW is output. 11. GBR [Output: bus arbitration] Outputs a global bus request signal. This signal indicates that the microprocessor is requesting the right to use the global bus. The signal is output when an interruption of interruption level 0 has occurred. 12. HREQ [Input: bus arbitration] Inputs a hold request signal given by an external device requesting the bus right. 13. HACK [Output: bus arbitration] Outputs a hold acknowledge signal indicating that the bus right is passed on to an external device. 14. RESET [Input: system control] Inputs a reset signal that resets the internal status of the processor. 15. HALT [Input/output (open drain): system control] Inputs and outputs a halt signal. When this signal is input, the current bus cycle is allowed to come to its end without subsequent entry into a new bus cycle. The signal is output in case of a system error. 16. FLAT [Input: system control] Inputs a float signal. When input, this signal unconditionally brings the external pins of the microprocessor to the high impedance state. The signal functions independent of other signals. 17. PURGE [Input: interruption, cache control] Inputs an internal cache purge signal given by an external device. This signal indicates that the external device is requesting the purge of the internal cache memory. When the request is serviced, all built-in cache memory of the CPU is purged. 18. NCA [Input/output (open drain): cache control] Inputs and outputs a non-cachable signal. While this signal is being input, no data is allowed to be taken into the internal cache. While the signal is being output, the NC (non-cachable) bit in the page table is made active upon access to the page that was set or upon output of an LOC signal. 19. IRLO-2 [Input: system control] Inputs an interrupt request signal. This is an interrupt request for use on any of the eight levels encoded with three signal conductors. Level 0, the highest level, is not masked for interruption. 20. BST [Input: system control] Inputs a bus status signal given by an external signal. When brought high, the signal indicates that the external device is in a normal bus cycle. When brought low, the signal indicates that something is wrong. The cause of the error is informed by a DTC half a clock signal later. 21. DCT [Input: system control] Inputs a data transfer complete type signal given by an external device. The signal is used by the external device to indicate the results of retries and bus access errors during bus transfer. 22. LOC [Output (tri-state): processor control] Outputs a bus lock signal indicating that a plurality of contiguous bus cycles cannot be divided. This signal is used during a read modify write cycle. The signal is output when an instruction BSETI, BCLRI or CSI is executed. 23. BAT0-2 [Output (tri-state): processor control] Output an access type signal indicating the type of the current bus cycle. 24. CPST0-2 [Input: processor control] Input a coprocessor status signal indicating the status of the coprocessor at a given point in time. 25. CDE [Output: processor control] Output a coprocessor data enable signal. The signal specifies that data is to be placed on the data bus in the next bus cycle. 26. CPDC [Input: processor control] Inputs a coprocessor data transfer complete signal. In a data read operation, the signal indicates that the coprocessor has placed effective data on the bus. In a data write operation, the signal indicates that the coprocessor has admitted data. 27. CLKf, 2f [Input: clock] Input a system clock signal. With the 20 MHz version, a 20 MHz clock signal is input by means of CLKf, and a 40 MHz clock signal is admitted using CLK2f. In Fig. 6, a coprocessor signal is identified by a diagonal grid pattern, and a data bus signal D0-D31 by a multiple slant pattern. As shown in Figs. 5 and 7, the right-hand side of the coprocessor semiconductor chip 25B principally comprises the external pins which receive the reference potential (GND) Vss, power supply potential Vcc, coprocessor signals and hold acknowledge signal HACK . The coprocessor signals comprise an address bus signal A27-A29, a byte control signal BC0 - BC3 , a bus start signal BS , a read/write signal R/ W , a bus access type signal BAT0-BAT2, a coprocessor data enable signal CDE , a coprocessor data transfer complete signal CPDC , a data transfer complete signal DC , and a coprocessor status signal CPST0-CPST2. In Fig. 7, each coprocessor signal is identified by a dot pattern ( ). An NC represents an unused external pin 25D (free pin). The address bus signal A27-A29, one of the coprocessor signals, is an input signal that provides an ID for selecting one of the coprocessors 25 through 28. It is assumed from now on that the coprocessor 25 has been selected by this signal. The byte control signal BC0 - BC3 is a signal that indicates in bytes the location of effective data on the data bus signal D0-D31. The bus start signal BS indicates the start of a bus cycle. The read/write signal R/ W is a signal that indicates the direction of data transfer, i.e., whether the microprocessor 24 reads data from an external memory or writes data thereto. The bus access type signal BAT0-BAT2 is a signal output by the microprocessor 24 indicating the type of access in effect. The coprocessor data enable signal CDE is a signal that starts a bus cycle of the microprocessor 24 one clock cycle after being asserted. This signal is given by the microprocessor as an output timing acknowledge signal. The retry signal RETRY is a signal that requests a retry upon error during the ongoing bus cycle. The coprocessor data transfer complete signal CPDC is a signal indicating the end of data transfer over the data bus between the microprocessor 24 and the coprocessor 25. The data transfer complete signal DC is a signal that indicates the end of data transfer over the data bus between the microprocessor 24 and the memory circuit 29, or between the coprocessor 25 and the memory circuit 29. The bus error signal BERR is a signal indicating that an error occurred during the ongoing bus cycle. The coprocessor status signal CPST0-CPST2 is a signal that indicates the internal operating status of the coprocessor 25. The hold acknowledge signal HACK is a signal indicating that the microprocessor 24 relinquished its bus right and entered a hold state. The reference potential Vss is the grounding potential for each circuit in the system, illustratively zero volt. The power supply potential Vcc is the operating potential for each circuit in the system, illustratively 5 volts. Both the reference potential Vss and the power supply potential Vcc are fixed to constant potential levels. The left-hand side of the semicondiictor chip 25B in Fig. 7 comprises the external pins 25D to which are applied such signals as the reference potential Vss, power supply potential Vcc, and clock signals CLKf and CLKf . A coprocessor ID signal CPID0-CPID2 supplies an identifier to the coprocessors 25 through 28 disposed in the electronic system 20. Each of the clock signals CLKf and CLKf is a reference signal that defines the timing for the internal operation of the system. The left-hand side of the semiconductor chip 25B also comprises the external pins 25D that handle the reset signal RESET , upper data signal UD, lower data signal LD, interrupt request signal IRL , and size-16 signal SIZ16. The reset signal RESET is a signal that stops all processing and initializes all registers in the system. The microprocessor 24 of this embodiment has its data bus signal formed of 32 bits. The upper data signal UP and the lower data signal LD are each an address signal used only when the data bus signal is set for 16 bits. The upper data signal UD is a switching signal that causes the high-order 16 bits of the data bus signal to be output. The lower data signal LD is a switching signal that causes the low-order 16 bits of the data bus signal to be output. The size-16 signal SIZ16 is an input signal that specifies whether the data bus signal is to be formed of 32 bits or 16 bits. The coprocessor and clock signal external pins 25D of the coprocessor are located in the same locations or on the same columns as, or on the adjacent columns of, the coprocessor and clock signal external pins of the microprocessor. For example, the byte control signal BC0-BC3 , one of the coprocessor signals, is assigned to the corresponding external pins at C4, B4, A4 and C5 of both the microprocessor and the coprocessor. The coprocessor data enable signal CDE , another coprocessor signal, is assigned to the same column 9, though it is not in the corresponding position. The bus access type signal BAT2, still another coprocessor signal, is assigned to the adjacent columns 6 and 7. In this manner, the external pins 24D and 25D for the clock and coprocessor signals of the microprocessor and coprocessor (signals common to the microprocessor and its coprocessor) are disposed in the same locations, on the corresponding columns, or on the adjacent columns in the package. This arrangement makes it possible, where the microprocessor and its coprocessor are linearly positioned on the board, to connect their corresponding external pins 24D and 25D linearly. The linear connection illustratively reduces skews in clock signals exchanged between the microprocessor and its coprocessor or between a plurality of coprocessors. Along the top and bottom sides of the semiconductor chip 25B are principally disposed the external pins 25D which receive such signals as the reference potential Vss, power supply potential Vcc, and data bus signal D0-D31. The data bus signal D0-D31 is a 32-bit input/output data signal. Data is exchanged between the data bus signal (D0-D31) pins of the coprocessor 25 on the one hand, and those of the microprocessor 24 or an external device, illustratively a memory, on the other. Of the external pins D0-D31 for the data bus signal, those to which bits D0-D15 are applied are located along the upper side of the semiconductor chip 25B; those to which bits D16-D31 are applied are located along the lower side of the semiconductor chip 25B. That is, the external pins 25D to which the data bus signal is applied are divided into two groups: one addressing the high-order 16 bits and the other dealing with the low-order 16 bits, located on the upper and lower sides of the chip each. In Fig. 7, a data bus signal D0-D31 is identified by a multiple-slash pattern (/////). As shown in Fig. 8, the semiconductor chip 25B of the coprocessor 25 has its sides lined with bonding pads BP, with circuits disposed within the sides. The semiconductor chip 25B comprises, among others, an I/O controller circuit 251, an operation circuit 252, an operation control circuit 253 and a multiplexer 254. The bonding pads along the periphery of the semiconductor chip 25B correspond in terms of locations to the external pins 25D shown in Figs. 5 and 7. The arrangement of the bonding pads is basically the same as that of the external pins. That is, along the right-hand side of the semiconductor chip 25B in Fig. 8 are principally disposed the bonding pads BP which are associated with coprocessor signals, just like the external pins 25D along the right-hand side of the base board 25A in Figs. 5 and 7. Likewise, the left-hand side of the semiconductor chip 25B has principally the external extension electrodes BP which are associated with the external pins 25D on the left-hand side of the base board 25A for such signals as clock signals CLKf and CLKf . Along the bottom side of the semiconductor chip 25B are also principally disposed the external extension electrodes BP which are associated with the external pins 25D for the data bus signal D0-D15 along the top side of the base board 25A. The top side of the semiconductor chip 25B also has principally the external extension electrodes which are associated with the external pins 25D for the data bus signal D16-D31 along the top side of the base board 25A. The external extension electrodes BP for the data bus signal D0-D31 are divided into two groups, as with the external pins 25D, to be separately disposed along the top and bottom sides of the semiconductor chip 25B in order to minimize signal delays by means of the connection over the shortest distances to the external pins 25D. In the arrangement described above, every second external extension electrode for the data bus signal D0-D31 is flanked on both sides by the external pins to which a fixed potential (Vcc or Vss) is applied. This construction prevents the generation of the noise attributable to potential fluctuations over the power supply wiring (Vcc or Vss) during a data bus operation. Of the external extension electrodes BP, those which are located in the middle of the left-hand side of the semicondiictor chip 25B and to which the clock signal CLKf is applied are each flanked on both sides by the external extension electrodes BP (in substantially square shape) to which the fixed potential Vcc or Vss is applied. The flanking external extension electrodes BP are connected to a power supply line 255 or 256 installed between the electrodes and the circuits therein. The power supply line 255 is illustratively made of aluminum, and is connected to the power supply potential Vcc. The power supply line 256 is illustratively made of aluminum as well, and is connected to the reference potential Vcc. The adding of the external extension electrodes BP to which the fixed potential is applied for noise prevention is not limited to those electrode to which the clock signal CLKf is applied; the electrodes with the fixed potential also flank each of the external extension electrodes BP handling coprocessor signals in the semiconductor chip 25B of this embodiment. As illustrated in Fig. 4, the external extension electrodes BP disposed along the sides of the semiconductor chip 25B are connected to the external pins 25D via bonding wires 25F, lead wires 25E, and through-hole wires (not shown). Meanwhile, the coprocessor of this embodiment would have preferably been mounted on a microprocessor chip. Instead, those functions that are difficult to incorporate in a single microprocessor chip due to constraints of the current production technology or to requirements in the degree of integration are implemented separately in a discrete LSI chip that operates on special control logic. This LSI chip constitutes each coprocessor that is closely coupled with the microprocessor and plays a significant role in executing the latter's instructions. Because the coprocessors 26 through 28 have substantially the same construction as the coprocessor 25, descriptions will not be repeated regarding the external pin arrangement and other related aspects of those coprocessors. As shown in Figs. 1, 2, 9 and 10, the microprocessor 24 and the coprocessors 25 through 28 are each mounted on the mounting surface 20D of the electronic system 20. Fig. 9 mainly depicts the coprocessor and clock signal conductors, and Fig. 10 shows these signal conductors and the bus lines together. In practice, the coprocessor signal external pins 24D and those 25D through 28D of the microprocessor 24 and the coprocessors 25 through 28, respectively, are arranged so as to fall on the same or the adjacent columns. This is because the microprocessor 24 and the coprocessors 25 through 28 are located on the mounting surface 20D in a substantially linear fashion. As shown in Figs. 9 and 10, the coprocessor signal external pins 24D and those 25D through 28D of the microprocessor 24 and the coprocessors 25 through 28, respectively, are electrically connected via coprocessor signal conductors 20A that stretch linearly on the mounting surface 20D. Likewise, the clock signal (CLKf) external pins 24D and those 25D through 28D are electrically connected via clock signal conductors 20B that extend linearly. The coprocessor signal conductors 20A and clock signal conductors 20B are each a conductor carrying a high-speed signal that determines how fast the electronic system 20 is to function. These signal conductors can be arranged in a substantially linear manner, as illustrated in Figs. 9 and 10. In particular, the clock signal (CLKf, CLKf ) conductors 20B are allowed to extend without crossing one another. In the meantime, the external pins to which data bus signals D0-D31 of the microprocessor 24 and of the coprocessors 25 through 28 are applied are electrically connected via bus lines (signal conductors) 20C, as shown in Figs. 1 and 10. The bus lines 20C are allowed to stretch on both sides of, and at certain distances from, the coprocessor signal conductors 20A and clock signal conductors 20B. Since the external pins (25D, etc.) to which the data bus signal D0-D31 is applied are disposed along the top and bottom sides of each of the semiconductor chips 24B through 28B, the bus lines 20C are allowed to extend along the top and bottom sides of each of the microprocessor 24 and coprocessors 25 through 28. Alternatively, the bus lines 20C may be located along the bottom edge of each of the microprocessor 24 and coprocessor 25 through 28 or in an outside area thereof. The mounting surface 20D illustratively comprises a six-tier conductor layer. The coprocessor signal conductors 20A, clock signal conductors 20B and bus lines 20C are each implemented in any of the six tiers that make up the signal conductor layer. In the electronic system 20, the first semiconductor device (PGA) acting as the microprocessor 24 and the second semiconductor device (PGA) as the coprocessor 25 (and/or 26 through 28) are mounted on the mounting surface 20D. In this setup, either the clock signal conductors 20B connected to the corresponding clock signal external pins (25D, etc.) of the first and second semiconductor chips, or the coprocessor signal conductors 20A connected to the corresponding coprocessor signal external pins of the same chips, are located on the mounting surface 20D in a substantially linear manner, as shown in Figs. 9 and 10. This arrangement reduces signal delays by shortening the clock signal conductors 20B or the coprocessor signal conductors 20A on the mounting surface 20D. The reductions in signal delays in turn translate into higher operation speeds of the electronic system 20. The first and the second semiconductor device have a plurality of external pins (25D, etc.) located on the base board (25A, etc.) along the sides of their respective semiconductor chips (25B, etc.). Along one side of each chip or the one opposite thereto are disposed the coprocessor or clock signal external pins. This makes it possible to locate these external pins in a substantially linear manner on the mounting surface 20D. Exchanges of the data bus signal D0-D31 and other control signals between the first and the second semiconductor device are performed over the bus lines 20C. As shown in Figs. 1 and 10, these bus lines 20C are disposed along and apart from the coprocessor signal conductors 20A and clock signal conductors 20B on the mounting surface 20D. This arrangement reduces the amount of cross talk that occurs between the coprocessor signal conductors 20A and the clock signal conductors 20B, thereby minimizing system malfunction of the electronic system 20 and boosting the electrical reliability thereof. As depicted in Figs. 7 and 9, the external pins (25D, etc.) located around the clock signal external pins (25D, etc.) of the first and the second semiconductor device are connected to the fixed potential Vcc or to ground. This arrangement causes the fixed potential to shield electromagnetically the surroundings of the clock signal external pins. This reduces the amount of noise generated in the clock signals CLKf and CLKf upon signal level changeover of the data bus signal D0-D31. Lowered noise levels in turn help significantly to prevent system malfunction of the electronic system 20 and to improve the electrical reliability thereof. As shown in Fig. 8, a fixed potential is connected to the bonding pads BP disposed around those (BP) to which the clock signals CLKf and CLKf are applied on each of the semiconductor chips (25D, etc.) of the first and the second semiconductor device. As in the foregoing arrangements, this also makes it possible to reduce the amount of noise generated in the clock signals CLKf and CLKf . Lowered noise levels help significantly to prevent system malfunction of the electronic system 20 and to improve the electrical reliability thereof. As depicted in Figs. 7 and 9, of the external pins (25D, etc.) of the coprocessors 25 through 28, those that extend close to the clock signal conductors 20B on the mounting surface 20D are connected to a fixed potential. That is, as opposed to the left-hand side of each of the coprocessors 25 through 28 having the external pins (25D, etc.) to which the clock signal CLKf is applied, the right-hand side of each coprocessor comprises the external pins to which a fixed potential is applied. As in the foregoing arrangements, this also reduces the amount of noise generated in the clock signals CLKf and CLKf over the clock signal conductors 20B on the mounting surface. Lowered noise levels help significantly to prevent system malfunction of the electronic system 20 and to boost the electrical reliability thereof. As illustrated in Figs. 9 and 10, in the electronic system 20 having the coprocessors 25 through 28 disposed on the mounting surface 20D, those clock signal conductors 20B of the coprocessors which are connected to the external pins (25D, etc.) receiving the clock signals CLKf and CLKf are located on both sides of, and in substantially parallel with, the clock signal external pins in the same direction. This arrangement reduces the amount of cross talk generated between the clock signal conductors 20B to which the clock signals CLKf and CLKf are applied. Lowered cross talk levels in turn improve the electrical reliability of the electronic system 20. It is to be understood that while the invention has been described in conjunction with a specific embodiment, it is evident that many alternatives, modifications and variations will become apparent to whose skilled in the art in light of the foregoing description. Accordingly, it is intended that the present invention embrace all such alternatives, modifications and variations. Illustratively, according to the present invention, coprocessors such as a memory management unit (MMU) and a decimal processing unit (DPU) may be incorporated in the electronic system 20 in place of the FPU's. Also according to the invention, the microprocessor 24 and the coprocessors 25 through 28 may be each replaced by a semiconductor device of a PLCC (plastic leaded chip carrier), QFP (quad flat package) or LCC (leadless chip carrier) construction. In other words, what may be called a four-side package having numerous external pins is suitable for embodying the invention. Also according to the invention, the number of the microprocessor and its coprocessors in the electronic system 20 is not limited to that of the preferred embodiment; the number may be varied in alternative embodiments. The principal benefit, among others, of the invention disclosed in this specification is twofold: the operation speed of the electronic system is boosted, and the electrical reliability thereof is improved.

Claims: An electronic system having a microprocessor (CPU) and a co-processor (FPU1) accommodated in pin grid arrays disposed on a circuit mounting board having conductive lines formed thereon, wherein said microprocessor (CPU) has a plurality of external pins (24D) located in a matrix pattern of rows and columns and connected to respective ones of said conductive lines, said external pins (24D) comprising first external pins carrying clock sianals (CLK) and coprocessor control signals; said co-processor (FPU1) is disposed adjacent said microprocessor (CPU) and has a plurality of external pins (25D) connected to respective ones of said conductive lines and located in a matrix pattern of rows and columns that are parallel to said rows and columns, respectively, of said microprocessor, said external pins of said co-processor (25D) comprising second external pins carrying said clock signals (CLK) and said coprocessor control signals whereby said first and second external pins are arranged such that corresponding ones of said first and second external pins are connected by selected ones of said conductive lines running linearly in the column direction. An electronic system according to claim 1, wherein said microprocessor (CPU) and co-processor (FPU1) each have m rows and n columns of external pins, said second external pins being located on one of the (ℓ-1)th, ℓ-th, and (ℓ+1) th columns when said first external pins are located on the ℓ-th column. An electronic system according to claim 2, wherein said second external pins are located on the ℓ-th column. An electronic system according to claim 3, wherein said second external pins are located on the k-th row when said first external pins are located on the k-th row. An electronic system according to any one of the preceding claims comprising: a further semiconductor device having a plurality of external pins in a matrix pattern of rows and columns that are parallel to said rows and columns, respectively, of said microprocessor and containing third external pins which provide said clock signal and coprocessor control signals; and further conductive lines electrically connecting said second and third external pins, said conductive lines and said further conductive lines running linearly in the column direction. An electronic system according to claim 5 as dependent on any one of claims 2 to 4, wherein said further semiconductor device has m rows by n columns of external pins, said second and third external pins being located on one of the (ℓ-1)th, ℓ-th and (ℓ+1)th columns when said first external pins are located on the ℓ-th column. An electronic system according to claim 6, wherein said second and third external pins are located on the ℓ-th column. An electronic system according to claim 7, wherein said second and third external pins are located on the k-th row when said first external terminals are located on the k-th row. An electronic system according to any one of the preceding claims, wherein said external pins (24D) of said microprocessor (CPU) further comprise fourth external pins which are connected to a fixed potential, wherein said fourth external pins are arranged close to said conductive line which is connected to the first external pin which carries said clock signal. An electronic system according to claim 9, wherein said fixed potential is either a reference potential or a power supply potential. An electronic system according to any one of the preceding claims, wherein said external pins (25D) of said co-processor (FPU1) which are close to said conductive lines carrying said clock signals are connected to a fixed potential. An electronic system according to claim 11, wherein said fixed potential is either a reference potential or a power supply potential. An electronic system according to claims 1 to 8, wherein said external pins (24D) of said microprocessor (CPU) further comprise fourth external pins which are connected to a fixed potential, wherein said fourth external pins are located around said first external pins carrying said clock signal. An electronic system according to claim 13, wherein said fixed potential is either a reference potential or a power supply potential. An electronic system according to any of claims 1 to 8, wherein said external pins (25D) of said co-processor (FPU1) further comprise fifth external pins which are connected to a fixed potential, wherein said fifth external pins are located around said second external pins carrying said clock signal. An electronic system according to claim 15, wherein said fixed potential is either a reference potential or a power supply potential.

Inventors: HASEGAWA ATSUSHI, NAITO MASAO, NAKAGAWA NORIO, OKAHASHI TATSUO, HASEGAWA, ATSUSHI, NAITO, MASAO, NAKAGAWA, NORIO, OKAHASHI, TATSUO
Applicants: HITACHI LTD, HITACHI MICROCOMPUTER SYST, HITACHI MICROCOMPUTER SYSTEM LTD., HITACHI, LTD.
Application year: 1989
Main classification: H01L25
IPC codes: H01L25, H01L23