Wichit Sirichote, wichit.sirichote@gmail.com
Build your own Microprocessor training kit with the 68008 Microprocessor. New interpreter language, Lox68k by Fred Bayer!
This is my 2016 year-end project. The educational kit using a 32-bit computing power, the Motorola 68008 microprocessor. The design is simple with minimum components, however providing a large amount of memory space, 128kB RAM and 128kB ROM. The keyboard and hex display allow us to enter 68000 code to the memory and test run with single step and break point. The CPU status will be saved to user registers for example D0-D7. These are 32-bits registers which can be displayed on the 8-digit seven segment directly. The decoder logics are put into the PLD chip, 22V10. All memory and I/O spaces, DTACK, AUTO vector, boot overlay signals, are written in logic equations. The monitor program was 'c' and assembly codes. Users may modify your own monitor program easily. The board layout is very nice, easy build, and easy use.
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| Hardware schematic (click to enlarge) |
Hardware descriptions: U6 is the 68008 microprocessor. The bus interface signals are A0-A19, and D0-D7.
The CPU clock is generated by Y1, the oscillator chip. The frequency is 10.000MHz.
U1 is 128kB EPROM, 27C010. The address space for EPROM is located at 0x40000-0x5FFFF. U2 is 128kB static RAM, 628128. The RAM space is located at 0x00000-0x1FFFF.
Power on reset will put the first 8 locations, 0 to 7 in ROM to be enabled. The ROM is enabled for that locations by the BOOT_VECTOR signal produced by the shift register, U7 74HC164. QH becomes HI, after 8 locations are fetched. The next cycle, will put RAM to the low address. This gives the interrupt vectors to be placed in RAM.
U5, memory and I/O spaces decoder chip is made with GAL20V10. It provides chip selected signals for memory and I/O chips, DTACK and VPA for auto vector generation.
U3, the 20-pin 89C2051 microcontroller chip produces 10ms tick. SW1 selects between 10ms tick or manual IRQ button. The chip uses E clock from 68008 which is 1MHz. The output from U4B is IPL1 signal. This is signal will be used to experiment the external interrupt level 2 with auto vector by VPA signal.
RESET signal is generated by Schmitt-trigger inputs trigger U4, R5 and C3. Q2 is voltage detector for brownout reset. The 68008 reset pin and halt pin are tied together. Q1 will pull it down when RESET1 signal is '0'.
U14, 74HC541 is 8-bit input port (PORT0). PA7 is one bit for serial data RXD signal. PA6 is for user key.
U11, 74HC573 is 8-bit output port (PORT2). The 8-bit output drives the 7-segment LED directly. No current limit resistor. U13 (PORT1) drives the BCD to decimal decoder chip, 74LS145. The active low output drives all 8 digit seven segment LED. The brightness is controlled by PWM. U13, pin 13 drives Q3 transistor for beep producing. Pin 12 is TXD pin.
U15,74HC573 is 8-bit output port (GPIO1 LED) for 8-bit binary number display. D14 lifts the forward biasing for proper brightness. JR1 is 16-pin socket for text LCD interface.
U16, MAX232 converts TTL level to RS232 level.
Q1, KIA7042 is reset chip for power brownout.
PLD equations : U5 is a PLD chip providing select signals for the memory, I/O ports, DTACK and VPA . The address and I/O spaces can be programmed using PLD equations. The PLD compiler is ATMELWinCupl. The output file, JEDEC will be used to program the PLD chip by a PLD programmer. All signals use FC0-FC2 as the main control.
Name 68008KIT ; /* *************** INPUT PINS *********************/
PIN 2 = AS;
PIN 3 = RW;
PIN 4 = A16;
PIN 5 = A17;
PIN 6 = A18;
PIN 7 = A19;
PIN 8 = FC0;
PIN 9 = FC1;
PIN 10 = FC2;
PIN 11 = A1;
PIN 13 = BOOT_VECTOR;
PIN 1 = E;
/* *************** OUTPUT PINS *********************/ PIN 14 = ROMCE;
PIN 15 = RAMCE;
PIN 16 = RAMWR;
PIN 17 = PORT0;
PIN 18 = PORT1;
PIN 19 = PORT2;
PIN 20 = LCD_E;
PIN 21 = GPIO1;
PIN 22 = VPA;
PIN 23 = DTACK;
ROMCE = ((FC2&FC1&FC0) # A19 # !A18 # A17 # AS) & BOOT_VECTOR; !RAMCE = !((FC2&FC1&FC0) # A19 # A18 # A17 # AS) & BOOT_VECTOR; !RAMWR = !((FC2&FC1&FC0) # A19 # A18 # A17 # AS # RW) & BOOT_VECTOR; !LCD_E = (FC2&FC1&FC0) # A19 # !A18 # !A17 # AS; !GPIO1 = (FC2&FC1&FC0) # !A19 # !A18 # !A17 # AS # RW # A1;
PORT0 = (FC2&FC1&FC0) # !A19 # A18 # A17 # A1 # AS # !RW;
!PORT1 = (FC2&FC1&FC0) # !A19 # A18 # A17 # !A1 # AS # RW; !PORT2 = (FC2&FC1&FC0) # !A19 # A18 # !A17 # AS # RW # A1; !VPA = (FC2&FC1&FC0); DTACK = (FC2&FC1&FC0);
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| PLD equations for 68008 kit. |
10ms System Tick: U3, 8051 compatible microcontroller is used to generate 10ms tick. The circuit runs with E clock from 68008 chip. The frequency is 10MHz/10. The tick signal is output at P3.7. TP1 is 50% duty cycle with frequency of tick/2. D1 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. We can use 10ms tick for experimenting with realtime OS as well.
; 10ms systemTick TIMER CHIP FOR 68008 KIT $mod52 dseg at 30h TICK: DS 1 cseg at 0
jmp main
org 00bh timer0_vector: JMP timer0_SERVICE
org 100h
;-----initialize data----------------------------- main: mov r7,#0 djnz r7,$ 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 FCBFH FOR 10ms INTERRUPT TIMER0_SERVICE:
PUSH ACC
ORL TH0,#0FCH
ORL TL0,#0BFH
CLR P3.7 ; produce interrupt trigger
;
SETB P3.7
CPL P1.6 ; CHECK TICK FREQUENCY must be 100Hz/2 INC TICK MOV A,TICK CJNE A,#100,SKIP MOV TICK,#0 Clr P1.7 MOV R7,#5 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: Motorola 68008P10
-Oscillator: 10MHz
-Memory: 128kB RAM, 128kB EPROM
-Memory and I/O Decoder chip: Programmable Logic Device GAL20V10D
-DTACK generation: zero wait state
-Display: high brightness 8-digit 7-segment LED
-Keyboard: 36 keys
-RS232 port: software controlled UART 2400 bit/s 8n1
-Debugging LED: 8-bit GPIO1 LED at location 0xF0000
-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: 300mA @7.5V AC adapter
-Expansion header: 40-pin header
