32-Bit Personal Computer Using a Bus Width Converter and a Latch for Interfacing With 8-Bit and 16-Bit Microprocessors

The present invention relates to a personal computer configured using a 32-bit microprocessor.

Various types of personal computers, each having a combination of an 8-bit MPU (Micro Processing Unit) and a peripheral LSI family, are available as low-end computer products. Middle-end personal computers employing 16-bit MPUs compatible with 8-bit MPU software have recently been developed and are becoming popular. The 8-bit models are gradually being replaced by 16-bit models, through utilizing a wealth of software created on the 8-bit MPU basis.

In addition, 32-bit MPUs have recently been developed to configure top-end personal computers. Demand has thus arisen for personal computers utilizing combinations of 32-bit MPUs and existing peripheral LSI families.

However, the development of 32-bit MPUs has been protracted, compared with that of 16-bit MPUs, for the following reason: It is difficult to design architecture for establishing compatibility between 8-, 16-, and 32-bit MPUs. Therefore, it is difficult to establish compatibility between 32- and 16-bit personal computers.

It is an object of the present invention to provide a simple, low-cost personal computer having a 32-bit microprocessor compatible with existing 16-bit personal computer software.

In order to achieve the above object of the present invention, there is provided a personal computer comprising:

a microprocessor unit having compatibility at least between 8, 16, and 32 bits; and

a peripheral-control large-scale integrated circuit arranged between the microprocessor unit and a peripheral device, and having a latch for latching 32-bit data from the microprocessor unit in units of 8 bits, an internal bus, a bus width-conversion function module for converting bus widths at least between 32 and 16 bits and between 32 and 8 bits, and peripheral device control modules, connected to the internal bus through the bus width-conversion function module, for controlling the peripheral device, the latch, the internal bus, the bus width-conversion function module, and the peripheral device control modules being formed on a single chip.

According to the present invention, a one-chip IC having the function module for converting the bus widths at least between 32 and 16 bits and between 32 and 8 bits, and the peripheral control function modules connected to the internal bus through the bus width-conversion function module, is arranged between the various peripheral devices and the 32-bit microprocessor compatible with existing 16-bit personal computer software, thereby realizing a personal computer. Therefore, a simple, low-cost, compact 32-bit personal computer compatible with existing 16-bit personal computer software can be provided.

Other objects and features of the present invention will be apparent from the following description taken in connection with the accompanying drawings, in which:

FIG. 1 is a block diagram of a personal computer according to an embodiment of the present invention;

FIG. 2 is a detailed block diagram of an 8- to 32-bit converter in FIG. 1; and

FIG. 3 is a detailed circuit diagram of a latch in FIG. 1.

FIG. 1 is a block diagram showing the main constituting components of a 32-bit personal computer according to an embodiment of the present invention.

MPU (Micro Processing Unit) 1 is compatible with 8-, 16-, and 32-bit MPU software. An iAPX386 available from Intel Corp., U.S.A. can be used as MPU 1. Computing processor (CO-PRO) 2 is an LSI having a floating computing function which is excluded from the functions of MPU 1. An iAPX387 available from Intel Corp., U.S.A. can be used as CO-PRO 2. Peripheral LSIs (VLSIA and VLSIB) 3 and 4 are arranged between MPU 1 and peripheral devices.

These peripheral LSIs can comprise combinations of VLSIs and discrete ICs, as in the conventional LSI family. More specifically, the peripheral LSIs are respectively VLSIs including personal computer control logic, excluding functions of MPU 1 and CO-PRO 2. These peripheral LSIs can be fabricated by integrated circuit techniques described in Japanese Patent Application Nos. 59-204462, 59-204455, and 59-204456. The constituent components in the peripheral LSIs will be described later. LSI (VLSIA) 3 controls and interfaces between the MPU bus and other devices, such as external devices and memories. LSI (VLSIB) 4 controls peripheral devices, such as a printer (PRT), a CRT display (CRT), an LCD display (LCD), and the like. Read-only memory (ROM) 5 is connected to the 8-bit bus in LSI 3, through a buffer (BUF), and stores BIOS (Basic I/O Software) and IPL (Initial Program Loader). Random-access memory (RAM) 6 is used as a main memory.

PPL (Phase Locked Loop) circuit 7 is connected to an FDD line connected to a floppy disk drive (FDD) as an external storage. Latch and buffer 8 stores a memory address, a memory read/write signal, an I/O read/write signal, and so on. Memory control circuit (DRAM-CONT) 9 is connected, in order to control RAM 6.

Circuit elements for controlling the peripheral devices connected to LSI 4 include character data-generating elements and an interface mechanism between LSI 4 and the peripheral devices. The character data-generating elements include: character-generator (CG-ROM) 11, character control RAM (CHR-CONT-RAM) 12, and attribute RAM (ATTRI-RAM) 13. The interface mechanism includes: video RAM (VIDEO-RAM) 14 and video controller (VIDEO-CONT) 15, both of which are arranged between peripheral LSI 4 and the CRT display (CRT); LCD interface (LCD-INTF) 16 arranged between LSI 4 and the LCD display (LCD); latch register (PRT-LATCH) 17 arranged between LSI 4 and the printer (PRT); and printer interface (PRT-INTF) 18. The personal computer in FIG. 1 also includes oscillator (OSC) 21 for generating operation clocks and clock generator (CLK-GEN) 22.

The operation of the personal computer having the arrangement described above will be described together with the internal components of LSI 3 and its function.

The 32-bit personal computer is operated according to the basic rules below:

(I) If a power switch is turned on, an initialize circuit of MPU 1 is activated. All other circuit blocks are reset in response to a reset signal from the initialize circuit.

After initialization, a start address is produced by MPU 1. A first instruction stored in ROM 5 is read out in response to the address signal and is fetched by MPU 1 through LSI 3. If a branch instruction is generated, the program is branched according to the condition represented by the branch instruction, and the program is sequentially executed.

(II) MPU 1 includes general registers, an arithmetic and logic unit (ALU), and arithmetic control logic circuits, such as a shifter, a memory protection control circuit, an instruction fetch-and-execution control circuit, and an instruction look-ahead buffer. Program execution and interrupt control are performed by MPU 1 (an individual LSI).

(III) Using the special circuit and program, computing processor (CO-PRO) 2 executes an instruction of a high order, such as a floating decimal instruction, which cannot be processed by MPU 1. A computed result is set in a general register in MPU 1. CO-PRO 2 receives from MPU 1 information representing MPU 1 fetching of an instruction to be executed by CO-PRO 2 from memory 5 and starts computation. The computed result is transferred from CO-PRO 2 to MPU 1.

(IV) Peripheral LSI (VLSIA) 3 is arranged between MPU 1 and other devices, such as the peripheral devices and the I/O interface including LSI 4 connected to the output of LSI 3, and controls the control signal flow and the data and address flow.

The constituent components of LSI (VLSIA) 3 will be described below:

a) Latch 301.

Latch 301 is connected to a combination of 16 and 8-bit data buses, one of which is directly connected to MPU 1, another of which is connected to a buffer which is then connected to MPU 1, and another of which is connected to a latch which is then connected to MPU 1. More specifically, latch 301 latches 32-bit data in units of 8 bits, i.e., in the form of four sets of 8-bit data. MPU 1 processes 32-bit data. LSI (VLSIA) 3 and the subsequent circuit blocks process 16- or 8-bit data. Therefore, software programmed by an 8- or 16-bit personal computer can be executed by a 32-bit personal computer.

b) Bus Width Converter (32 bits .rarw..fwdarw.8 bits) 302.

In order to maintain compatibility of the 32-bit processor with 8- or 16-bit computer software, converter 302 controls the bus width. Converter 302 selects one of the 8-bit data bytes from the 4.times.8 bits (=32 bits) to maintain compatibility with 8-bit computer software. Converter 302 also selects upper or lower 16-bit data among 32 bits to maintain compatibility with 16-bit computer software.

c) Bus Controller (BUS-CONT) 303.

Bus controller 303 decodes a bus control signal (the type of data on the data bus) from MPU 1 and the direction (i.e., read/write). The decoded data is sent to the subsequent interface.

d) DMA Controller (DMA) 304.

DMA controller 304 transfers data and the program between MPU 1 and the memories, as well as data between I/O devices and the memory. Controller 304 selectively assigns the data bus to MPU 1 or the I/O, so as to transfer data between the I/O device and the memory.

e) Page Register (PAGE-REG) 305.

The I/O device usually transmits/receives 8-bit data (e.g., in units of ASCII codes). Page register 305 is preferably connected to a 8-bit bus.

32-bit data from MPU 1 is input to page register 305, and 32-bit data from register 305 is sent to MPU 1. In other words, 4 bytes are simultaneously input to or output from page register 305. Register 305 accesses the addressed of one of the four bytes.

f) Timer Circuit (TMR) 306.

Clock information is required in the peripheral devices or the like. Software timer 306 is arranged to arbitrarily set a time unit (e.g., milliseconds), and can be externally operated. In this embodiment, four timers are arranged thus.

g) Programmable Interrupt Controller (PIC) 307.

Programmable interrupt controller 307 controls interrupt priority and mask conditions.

h) Floppy Disk Controller (FDC) 308 and FDC Interface (FDC-INTF) 309.

Floppy disk controller 308 is a circuit for controlling input/output of a floppy disk. FDC interface 309 is a buffer register for interfacing with floppy disk drive (FDD) (not shown).

i) Transfer Control Register (SW-REG) 310.

Transfer control register 310 is a buffering register for controlling transfer of 32- or 8-bit data.

j) Parity Check Circuit (PARITY-CHECK) 311.

Parity check circuit 311 detects a parity error on the data bus and generates a parity bit.

k) Word/Byte Controller (WORD.fwdarw.BYTE) 312 and Wait Controller (WAIT-CONT) 313.

Word/byte controller 312 controls switching between 8- and 16-bit data. Wait controller 313 controls timings for minimizing the memory access wait time.

l) Memory-I/O.Address-Decode Circuit (MEM-I/O.ADR-DECODE) 314, Refresh Address Circuit (REFRESH-ADRS) 315, Memory Address Selector (D-RAM REFRESH ADRS-SELECT) 316, and Memory Address Buffer (BUF) 317.

These circuits perform refresh control, address decoding (including control of RAS and CAS signals), and memory access control, such as read/write mode control, if the main memory comprises a dynamic RAM (D-RAM).

The circuits in items (a) through (i) above are integrated on a single LSI as LSI 3. LSI (VLSIA) 3 deals with the respective circuit blocks as macro cells. These cells are formed on a single chip by superintegration (SI) techniques.

(V) Peripheral LSI (VLSIB) 4.

Peripheral LSI (VLSIB) 4 has an internal function logic different from that of LSI (VLSIA) 3. LSI 4 directly controls the printer (PRT), the CRT display (CRT), the LCD display (LCD), character generator (CG-ROM) 11 for generating kanji characters, and the like. VLSIB 4 can be connected to the printer (PRT) (not shown) through latch register (PRT-LATCH) 17. VLSIB 4 can also be connected to the CRT display (CRT) (not shown) through video RAM (VIDEO-RAM) 14 and video controller (VIDEO-CONT) 15, and to the LCD display (LCD) (not shown) through LCD interface (LCD-INTF) 16. VLSIB 4 transfers data including the kanji codes to these display devices. The kanji code has a font conversion function, so as to vertically or horizontally display the characters. Display modifications (enlargement, reduction, rotation, etc.) can be performed on the CRT display.

(VI) Memory

Memories comprise ROM 5, RAM 6, and the like.

ROM 5 stores BIOS (Basic I/O Software), IPL (Initial Program Loader), and so on.

(VII) Clock Generator (CLK-GEN) 22.

Clock generator 22 is a circuit for clocking the personal computer as a whole.

A buffer (BUF) is connected to the memory bus to achieve external expansion without modifications.

FIG. 2 is a detailed block diagram of bus width converter 302 in FIG. 1. Referring to FIG. 2, the bus width converter comprises 16-bit line driver/receiver 302.sub.1, and the 8-bit line drivers/receivers 302.sub.3, 302.sub.4, and 302.sub.5. Read/write direction control and strobe signals are supplied to each of drivers/receivers 302.sub.1, 302.sub.3, 302.sub.4, and 302.sub.5. Driver/receiver 302.sub.1 is arranged to output 16-bit data upon reception of the upper bits 16-31 of data from MPU 1. Driver/receivers 302.sub.3 and 302.sub.4 are arranged to output parallel 16-bit data upon reception of the lower bits 0-15 of data bits from MPU 1. Driver/receiver 302.sub.4 and 302.sub.5 are each arranged to output serial 8-bit data upon reception of the lower bits 0-15 of data from MPU 1. More specifically, the lower 8 bits of data 0-7 is output through driver/receiver 302.sub.4, and the upper 8 bits of data 8-15 is output through driver/receiver 302.sub.5.

FIG. 3 is a detailed circuit diagram of latch 301 and converter 302 in FIG. 1. Referring to FIG. 3, latch 301 comprises two 8-bit line drivers/receivers 301.sub.3 and 301.sub.4 and 16-bit driver/receiver 301.sub.1. Read/write direction control signals are respectively supplied to drivers/receivers 301.sub.1, 301.sub.3, and 301.sub.4, and outputs therefrom are connected as 32-bit data to be input into an external 32-bit memory or sent along the main bus of another system. The outputs from drivers/receivers 301.sub.1, 301.sub.3, and 301.sub.4 are also connected to bus width converter 302. If converter 302 outputs 8-bit data, it enables one of drivers/receivers 302.sub.3 or 302.sub.4. However, if converter 302 outputs the lower 16 bits of data 0-15 in parallel, it enables both drivers/receivers 302.sub.3 and 302.sub.4. In addition, if 16-bit serial data is to be generated, bits 8 through 15 are output through driver/receiver 302.sub.5, and bits 0 through 7 are output through driver/receiver 302.sub.4. First, driver/receiver 302.sub.4 is enabled and driver/receiver 302.sub.5 is disabled by MPU 1. Thereafter, driver/receiver 302.sub.4 is disabled and driver/receiver 302.sub.5 is enabled.

The 32-bit personal computer can be made compact, since it comprises MPU 1, computing processor 2, peripheral LSI 4, ROM 5, and RAM 6, as the major constituent components.

By utilizing the 32-bit functions of MPU 1, the internal logic functions of the personal computer, including the bus width-conversion function of peripheral LSI (VLSIA) 3, allow connections with 16- or 8-bit external devices. Therefore, the 32-bit personal computer can be compatible with existing 8- and 16-bit personal computer software, and the overall system can be simple and inexpensive.

It will be apparent to those skilled in the art that various modifications and variations can be made in the personal computer of the present invention without departing from the scope or spirit of the invention. For example, various implementations of latch 301 can be used to latch 32-bit data in units of 8 bits. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.