Wichit Sirichote, wichit.sirichote@gmail.com
Build your own Microprocessor training kit with the 80C88 CMOS Microprocessor. Updated monitor program!
Simple design single board computer using the 80C88 16-bit microprocessor. The CPU is Harris 80C88 40-pin ceramic package. The oscillator chip is Siemens SAB8284B with 12MHz xtal. The CPU clock is 4MHz. The ROM is now at the highest memory space designed for boot loader with lowest location for running application programs in RAM space. Learn the basic of x86 CPU with this trainer kit is very fun.
The board consumes approx. 180mA at +5V power supply. Most chips produce no heat, only 8284 and 7805 are a bit warm.
The software UART, 2400 bit/s is for Intel hex file downloading.
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| Hardware schematic (click to enlarge) |
Hardware descriptions: U5 is CMOS 80C88 microprocessor in minimum mode. The Address bus is demultiplexed with ALE signal and latched by U6 and U9, 74HC573.
The CPU clock is generated by U8, 8284 chip. The Xtal frequency is 12.000MHz. CPU clock is 12.000MHz/3 = 4.000MHz.
U1 is 32kB EPROM, 27C256. The address space for EPROM is decoded at 0xFC000-0xFFFFF. U2 is 128kB static RAM, 628128. The RAM space is located at 0x00000-0x1FFFF.
U3, memory and I/O spaces decoder chip is made with GAL16V8D. It provides chip selected signals for memory and I/O chips.
U4, the 20-pin 89C2051 microcontroller chip produces 10ms tick. SW1 selects between 10ms tick or manual INTR button. The chip uses PCLK from 8284 chip.
U15, 74HC541 is 8-bit input port (PORT0). PA7 is one bit for serial data RXD signal.
U13, 74HC573 is 8-bit output port (PORT2). The 8-bit output drives the 7-segment LED directly. No current limit resistor. U14 (PORT1) drives 6-digit common cathode pin. The brightness is controlled by PWM.
U16, 74HC175 is 4-bit output port (PORT3). Bit 3 is for TxD serial data stream. Bit 4 is for BEEP driver.
U17, 74HC573 is 8-bit output port for 8-bit binary number display. D15 lifts the forward biasing for proper brightness. JR1 is 16-pin socket for text LCD interface. U18, MAX232 converts TTL level to RS232 level.
Q1, KIA7042 is reset chip for power brownout.
PLD equations : U3 is a PLD chip used to select the memory and I/O ports. The address and I/O spaceS can be programmed using PLD equations. The source file of PLD equations is shown in Figure 4. The PLD compiler is ATMELWinCupl. The output file, JEDEC will be used to program the PLD chip by a PLD programmer.
Name 8088KIT ; /* *************** INPUT PINS *********************/ FIELD ADDRESS = [A15..A12]; /* *************** OUTPUT PINS *********************/ ROMCE = IOM # !A17 # !A18 # !A19; RAMCE = IOM # A17 # A18 # A19; PORT0 = RD # !IOM # !A8 # A9 # A1 # A0; !LCD_E = (RD & WR) # !IOM # A8 # !A9; !GPIO1 = WR # !IOM # A8 # A9 # A1 # A0; !PORT1 = WR # !IOM # A8 # A9 # A1 # !A0; !PORT2 = WR # !IOM # A8 # A9 # !A1 # A0; PORT3 = WR # !IOM # A8 # A9 # !A1 # !A0; |
| PLD equations for 8088 kit. |
10ms System Tick: U16, 8051 compatible microcontroller is used to generate 10ms tick. The circuit runs with TTL clock from 8284 chip. The frequency is 12MHz/2. The tick signal is output at P3.7. TP1 is 50% duty cycle with frequency of tick/2. D13 is for indicating tick signal. Calibrating the correct tick frequency can be done by testing the pulse frequency at TP1.
The source code was written in assembly code. The sample below produces a fixed frequency 100Hz or 10ms tick.
$mod52 dseg at 30h TICK: DS 1 cseg at 0
jmp main
org 00bh timer0_vector: JMP timer0_SERVICE
org 100h
;-----initialize data----------------------------- main: mov r7,#0 djnz r7,$ mov sp,#60h ; set stack pointer to 60h MOV P1,#0FFH MOV TICK,#0 mov tmod,#1 ; set timer mode 1 setb et0 ; enable timer0 interrupt setb ea ; enable all interrupt setb tr0 ; run timer0 SJMP $ ; RELOAD FA2CH FOR 10MS INTERRUPT TIMER0_SERVICE:
PUSH ACC
ORL TH0,#0F9H
ORL TL0,#07DH ; COMUPTED VALUE IS F97DH
; CPL P3.7
CLR P3.7 ; produce interrupt trigger to Z80
NOP
; NOP
; NOP
; NOP
SETB P3.7
CPL P1.6 ; CHECK TICK FREQUENCY INC TICK MOV A,TICK CJNE A,#100,SKIP MOV TICK,#0 Clr P1.7 MOV R7,#30 DJNZ R7,$ SETB P1.7 SKIP: READ_MORE: POP ACC RETI end
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| Source code listing of 10ms tick generator. |
Hardware Features:
-CPU: Harris 80C88 CMOS Microprocessor 4MHz
-Oscillator: 8284
-Memory: 128kB RAM, 32kB EPROM
-Memory and I/O Decoder chip: Programmable Logic Device GAL16V8D
-Display: high brightness 6-digit 7-segment LED
-Keyboard: 32 keys
-RS232 port: software controlled UART 2400 bit/s 8n1
-Debugging LED: 8-bit GPIO1 LED at location 00H
-Tick: 10ms tick produced by 89C2051 for time trigger experiment
-Text LCD interface: direct CPU bus interface text LCD
-Brownout reset: KIA7042 reset chip for power brownout reset
- Power consumption: 180mA @7.5V AC adapter
-Expansion header: 40-pin header
