Wichit Sirichote, wichit.sirichote@gmail.com
New design with the 8086 16-bit microprocessor. Best for learning the x86 instructions and hardware.
The 8086 microprocessor kit is another kit suggested by Francesco from Italy. The kit uses 8086, real 16-bit microprocessor. This kit has 16-bit EPROM for the monitor program, two 628128 SRAM for application program, 8250 UART chip for serial port. The platform is similar to all of my designs with 10ms tick generator for timer interrupt testing. I used GAL22V10, 24-pin PLD for memory and I/O decoders. Some hardware was similar to 8088 kit. With the 16-bit data bus, all I/O devices are located in EVEN addresses. The size is a bit bigger than 8-bit kits.
The 8086 kit is the best tool for learning the low level CPU operations of the popular x86 based microcomputer. Kit is available on eBay for both DIY and prebuilt.
The kit draws much power compare to the 8-bit. I decided to put the 7805 on board the same as 8-bit kit. This kit will need heatsink on the 7805.
The 8250 UART, provides 9600 bit/s for Intel hex file downloading and serial monitor commands.
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| Hardware schematic (click to enlarge) |
Hardware description: The 8086 CPU, U6 is minimum mode configuration. U7,U9,U10 74HC573 8-bit latch, demultiplexs 20-bit address bus.
The CPU clock is generated by U8, 8284 chip. The Xtal frequency is 14.7456MHz. CPU clock is 14.7456MHz/3 = 4.9152MHz. PCLK is 2.4576MHz for UART chip.
CPU clock measured at pin 8, 8284 chip (4:6).
Peripheral Clock, PCLK measured at pin 2, 8284 chip.
U1 is 16-bit 128kword EPROM, 27C1024. The address space for EPROM is decoded at 0xC0000-0xFFFFF. U2 is 128kB static RAM, 628128 for LOW BYTE and U3 is for HIGH BYTE. The RAM space is located at 0x00000-0x3FFFF.
With the 16-bit bus, A0 is not used for addressing. CPU will access 16-bit locations using even address only.
U11, memory and I/O spaces decoder chip is made with GAL22V10. It provides chip selected signals for memory and I/O chips.
U5, the 20-pin 89C2051 microcontroller chip produces 10ms tick. SW1 selects between 10ms tick or manual INTR button. The chip uses PCLK, 2.4576MHz 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 : U11 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 8086KIT ; /* *************** INPUT PINS *********************/ /* *************** OUTPUT PINS *********************/ PIN 14 = ROMCE; PIN 16 = RAM_HI; ROMCE = !IOM # !A18 # !A19; RAM_LOW = !IOM # A18 # A19 # A0; RAM_HI = !IOM # A18 # A19 # BHE; !GPIO1 = WR # IOM # A10 # A9 # A8 # A7 # A0; PORT0 = RD # IOM # A10 # A9 # !A8 # A7 # A0; !PORT1 = WR # IOM # A10 # A9 # !A8 # !A7 # A0; !PORT2 = WR # IOM # A10 # !A9 # A8 # A7 # A0; PORT3 = WR # IOM # A10 # !A9 # A8 # !A7 # A0; UART = IOM # A10 # !A9 # !A8 # A7 # A0; !LCD_E = (RD & WR) # IOM # !A10 # A9 # !A8 # A7; |
| PLD equations for 8086 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 2.4576MHz. The tick signal is output at P3.7. TP1 is 50% duty cycle with frequency of tick/2. D1 is for indicating tick signal.
The source code was written in assembly code. The sample below produces a fixed frequency 100Hz or 10ms tick.
; 10ms systemTick TIMER CHIP FOR 8086 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 FA2CH FOR 10MS INTERRUPT TIMER0_SERVICE:
PUSH ACC
ORL TH0,#0F8H
; ORL TL0,#07DH ; COMUPTED VALUE IS F800H
; CPL P3.7
CLR P3.7 ;
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 |
| Source code listing of 10ms tick generator. |
Hardware Features:
-CPU: 8086 16-bit microprocessor
-Oscillator: 8284, clock generator XTAL 14.7456MHz
-Memory: 256kB RAM, 256kB EPROM
-Memory and I/O Decoder chip: Programmable Logic Device GAL22V10
-Display: high brightness 6-digit 7-segment LED
-Keyboard: 32 keys
-RS232 port: 8250 UART 9600 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: 500mA @9.0VDC AC adapter
-Expansion header: 40-pin header
-Mechanical: 178x184 mm size, 250 Grams (fully assembled)
Monitor commands features:
