There are a lot of old develop boards for all kinds for cpu’s.
These where build to learn machine code programming. Mostly made in the 80’s, and based on populair cpu’s at that time.
I own a some of these SDK’s (System Design Kits)
8085 – SDK85 i bought recently 8085 CPU
Microprofessor-1 (MPF-1) Z80 CPU
And my own 680x based computer
Most of these use a keyboard scanner which is also connected to 7 segment displays.
The way they work is practically the same. There is a VIA or PIA. Versitile interface adaptor, or Peripheral interface adaptor. These have two times 8 bits to control devices. When using 4 bits and convert these to 16 lines by using a 75ls145 for example. If you put a counter on those 4 bits, you sequently activate 1 of 16 lines. These lines you can use to scan a keyboard matrix OR display a character on a 7 segment display. These display’s won’t hold the data (and show the character) when not activated. The trick is to update de display fast enough so you don’t see the flickering on/off.
Activate a line and read a byte with the VIA = Reading keyboard row Activate a line and write a byte with the VIA = Display on a segment
These VIA/PIA’s where made with specific timings to match the CPU. 6522/6820/8255
Below you see some different implementations of these keyboard/display combo’s
Thaler 6502 kit
Microprofessor MPF-1 kit (ignore red circle)
SDK85 kit
Eltec 6800
My version using darlington arrays (ULN2003)
When looking at the 8085 version you see transistors being a ULN2003 is a chip with those transistors/amplification enclosed. It doesn´t draw much current from the bus, and diodes protect the way the current flows.
Buzzer and led on VIA 2, blinky and sound timed by the internal timers of the 6522
ACIA testing still going on, writing software
Mini matrix keyboard removed, and used the temporary cursor buttons for the test with a rom which allows for a 8bits upload method using a arduino and the 6522. (I’m working on the big keyboard)
Work in progress code
PORT2B = $5000 ; VIA PORTB
PORT2A = $5001 ; VIA PORTA
DDR2B = $5002 ; Data direction register
DDR2A = $5003 ; Data direction register
PORTB = $6000 ; display
PORTA = $6001 ; control display + matrix keyboard
DDRB = $6002 ; data direction register
DDRA = $6003 ; data direction register
SID = $7000 ; sid base address
E = %10000000 ; enable bit
RW = %01000000 ; RW bit
RS = %00100000 ; Register Select bit
HOME = %00000010 ; VIA PORTB HOME command
DADDR = %00010000 ; VIA DADDRESS
LINENO = $0200 ; temp address linenumber (move to other location)
NEXTLINE = 40 ; 2x16 Chars but internally 40
.org $8000
reset:
ldx #$ff
txs ; reset stack
; ###################################################
; # DISPLAY CONTROL #
; ###################################################
; VIA Setup
lda #%11111111 ; Set all pins on port B to output
sta DDRB
lda #%11100000 ; Set top 3 pins on port A to output
sta DDRA
; DISPLAY Setup
lda #%00111000 ; Set 8-bit mode; 2-line display; 5x8 font
jsr lcd_instruction
lda #%00001110 ; Display on; cursor on; blink off
jsr lcd_instruction
lda #%00000110 ; Increment and shift cursor; don't shift display
jsr lcd_instruction
lda #$00000001 ; Clear display
jsr lcd_instruction
; ###################################################
; # PRINT MESSAGE LINE NO 0 #
; ###################################################
lda #0 ; set line number
sta LINENO ; store for subroutine
jsr gotoline ; move cursor
ldx #0 ; message index pointer
print:
lda message0,x ; start of message
beq nextprint ; stop when null in message (asciiz <- Zero padded)
jsr print_char ; print char
inx ; incr index
jmp print ; resume print
; ###################################################
; # PRINT MESSAGE LINE NO 1 #
; ###################################################
nextprint:
lda #1 ; set line number
sta LINENO ; store
jsr gotoline
ldx #0 ; index pointer
print2:
lda message1,x ; absolute address message + x in A
beq sidsound ; if x is 0, end of message
jsr print_char ; jump subroutine
inx ; increment x
jmp print2 ; loop print2
; ###################################################
; # SID SOUND #
; ###################################################
sidsound:
lda #0
sta SID+$5 ; attack/decay duration
lda #250
sta SID+$6 ; sustain level/release duration
lda #$95 ; frequency voice 1 low byte
sta SID+$0
lda #$44 ; frequency voice 1 high byte
sta SID+$1
lda #%00100001 ; sawtooth + gate
sta SID+$4 ; control register voice 1
lda #$0f ; filter mode and volume (bits 3-0 main volume)
sta SID+$18 ; filter mode and volume
; ###################################################
; # 2ND VIA #
; ###################################################
lda #%11111111 ; set port A output
sta DDR2A
lda #%11111111 ; all ones!
sta PORT2A
; ###################################################
lda #%11111111 ; set port A output
sta DDR2A
lda #%11111111 ; all ones!
sta PORT2A
; ###################################################
; # MAIN PROGRAM LOOP #
; ###################################################
loop:
jmp loop
; 1234567812345678
message0: .asciiz "VIA 1,2 SID TEST"
message1: .asciiz " FASH 2022 "
; ###################################################
; # ONLY SUBROUTINES #
; ###################################################
; ###################################################
; # Subroutine gotoline #
; # Moves character placement position on display #
; # Needs : $LINENO ADDRESS #
; # Exit values : - #
; # Destroys registers: - #
; ###################################################
gotoline:
pha ; store a
txa
pha ; store x
ldx LINENO
lda #HOME ; cursor down
jsr lcd_instruction
lda #$80
nextline:
ldx LINENO
cpx #00
beq endnextlines
loopline:
adc #40
jsr lcd_instruction
dex
stx LINENO
jmp nextline
endnextlines:
pla ; pop a
tax ; a to x
pla ; pop a
rts
; ###################################################
; # LCD SUBROUTINES #
; ###################################################
lcd_wait:
pha
lda #%00000000 ; Port B is input
sta DDRB
lcdbusy:
lda #RW
sta PORTA
lda #(RW | E)
sta PORTA
lda PORTB
and #%10000000
bne lcdbusy
lda #RW
sta PORTA
lda #%11111111 ; Port B is output
sta DDRB
pla
rts
lcd_instruction:
jsr lcd_wait
sta PORTB
lda #0 ; Clear RS/RW/E bits
sta PORTA
lda #E ; Set E bit to send instruction
sta PORTA
lda #0 ; Clear RS/RW/E bits
sta PORTA
rts
print_char:
jsr lcd_wait
sta PORTB
lda #RS ; Set RS; Clear RW/E bits
sta PORTA
lda #(RS | E) ; Set E bit to send instruction
sta PORTA
lda #RS ; Clear E bits
sta PORTA
rts
nmi:
rti
irq:
rti
.org $fffa
.word nmi
.word reset
.word irq
; .word $0000
In this case designed for my 6502, but it is a generic setup.
I it just a dual 16key matrix decoder merged together. You can probably use this with raspberries, arduinos etc.
I wanted to use 74C923 but these are nowhere to be found. And even then, the number of keys wil be 20. So i am tying together two 74C922 using some logic in a PLD.
First draft
It wil be something like above. Using the data availabe signal i can combine both 16key matrixes. (In theory .. it is all untested)
New address decoder in place! Connected RAM/ROM/SID/VIA1/VIA2 and ACIA
ROM
8000-FFFF
SID
7000-700F (sound)
VIA1
6000-60xx (Hex key matrix)
ACIA
6800-68xx (serial)
VIA2
5000-50xx (led test at the moment)
RAM
0000-3FFF
To plan: Bigger maxtrix keyboard and other displays
ACIA 6551
Got a serial connection working between the 6502 and my linux machine!
3 line serial – no hardware handshake
At the moment when a reset occurs , hello is being printed. Text typed in the minicom terminal, is echo-ed back and displayed on the LCD display.
Things learned: Do not trust internet schematics blindly!
The crystal used for the ACIA (pin 6/7 1.8432Mhz needs a 1M ohm resistor parallel over the crystal, and a 30nF capacitor from pin 7 to GND
When using a terminal emulator, and using 3 wires. Disable hardware handshake.
Keyboard rewired.
What didn´t work as planned:
New amplifier schematic for the SID. There is too much noise.
Amplifier with a LM628
Bought a dual power supply (5V and 12V). But this one has a lot of signal noise on the SID part and even my battlestation speakers!
LED test 2nd via
PORTB = $5000 ; VIA PORTB
PORTA = $5001 ; VIA PORTA
DDRB = $5002 ; Data direction register
DDRA = $5003 ; Data direction register
LED = %10000000
.org $8000
reset:
lda #%11100000 ; Set top 3 pins on port A to output
sta DDRA
lda LED
sta PORTA
loop: ; done loop until doomsday
jmp loop
irq:
nmi:
.org $fffa
.word nmi
.word reset
.word irq
ACIA part
ACIA_RX = $6800
ACIA_TX = $6800
ACIA_STATUS = $6801
ACIA_COMMAND = $6802
ACIA_CONTROL = $6803
lda #$00
sta ACIA_STATUS
lda #$0b
sta ACIA_COMMAND
lda #$1f
sta ACIA_CONTROL
The ATF22V10 is a Programmable Logic Device. This means you can program the logic in the chip.
Internally it looks like a big matrix of connections which you can program to connect/disconnect from certain logic.
It has just a bunch of inputs/outputs
So if we want to have a 7 Segment decoder (you can easily buy a BCD decoder .. but these only work for displaying 0-9 and not 0-9A-F for displaying HEX numbers)
7 Segment display
Binary IN
7 Segment decoded
Displays
D C B A
A B C D E F G
0 0 0 0
1 1 1 1 1 1 0
0
0 0 0 1
0 1 1 0 0 0 0
1
0 0 1 0
1 1 0 1 1 0 1
2
0 0 1 1
1 1 1 1 0 0 1
3
0 1 0 0
0 1 1 0 0 1 1
4
0 1 0 1
1 0 1 1 0 1 1
5
0 1 1 0
1 0 1 1 1 1 1
6
0 1 1 1
1 1 1 0 0 0 0
7
1 0 0 0
1 1 1 1 1 1 1
8
1 0 0 1
1 1 1 1 0 1 1
9
1 0 1 0
1 1 1 0 1 1 1
A
1 0 1 1
0 0 1 1 1 1 1
B
1 1 0 0
1 0 0 1 1 1 0
C
1 1 0 1
0 1 1 1 1 0 1
D
1 1 1 0
1 0 0 1 1 1 1
E
1 1 1 1
1 0 0 0 1 1 1
F
Now we see that segment A is 1 in the case of (0,2,3,5,6,7,8,9,A,C,E,F)
When programming the PLD we can write that as: (note / means inverted a plus is OR, and * is AND) So A is 0 in case of input being (1,4,B,D)
Made a simulation of my new address decoder. It uses a 74LS138 and a bunch of NAND gates. You can safe using 4 NAND gates if you are not going to use split IO
Address
8000-FFFF
ROM
ROM
7000-7FFF
Sound chip
SID
6000-6FFF
Display + cursor
VIA1
5000-5FFF
Keymatrix
VIA2
4800-4FFF
split io
IO
4000-47FF
split io
IO – ACIA
0000-3FFF
Uses clock
RAM
Above part is a single chip 74LS138
UPDATE: Found some 74LS139, so i could have changed some things around.
I found some stuff while sorting out some old computer stuff. Way back, when my Amiga was my main computer, i wanted to make my own version. A modular one.
So i started to segmentize the amiga, to put it on several exchangeable cards.
Eurocards are standardized prints 150mm x 100mm, mostly with a DIN41612 connector.
DIN41612
Eurocard example
When you make modules you can change/upgrade/test, you can have a very easy interchangeable system using a backplane like this
So i started planning those modules:
CPU – 68000 but upgradeable to 68030 or alike
Memory – With expansion
Sound
Video
More IO possibilities
Keyboard (see more at the bottom of this page)
I had a nice case which could hold a big backplane, custom powersupply. And a front panel containing drives, leds and knobs. (I know i have more info on this somewhere on my fileserver)
A nice example picture i found on danceswithferrets website
I never finished this project. I used Tech Manuals and print layouts to understand how things where done.
Part of schematic
I started to draw the modules like they where placed on the print on semi transparent (chalk)paper, the kind of paper that was used for electronic and mechanic diagrams.
TOP Part of printBottom part of printBoth on top of eachother
Above is my design for a hex keyboard to enter opcodes in hex using a simple monitor program. i used a 74ls922 which can decode a 4×4 matrix. I’d rather had a 74ls723 which can encode 20 keys.
Nowhere to be found. So i have to think of a new plan.
Now it is configured as follows:
C
D
E
F
8
9
A
B
4
5
6
7
0
1
2
3
When pressing the alternate key
addr (to implement)
run (1/2 implemented)
reset (to implement)
step instruction (to implement)
memory next
memory previous
PCB design for matrix hexboard with place for notes
Meanwhile i’ve ordered new keys (the ones i’ve been using for my photomanager project and wnat to have a setup like this:
?
?
addr
run
reset
C
D
E
F
?
8
9
A
B
step
4
5
6
7
mem next
0
1
2
3
mem prev
When you want to show the status of busses and alike, you can’t use a led and restistor directly on the bus, it will require too much current. So i’ve been using below schematic which uses a darlington array.
Now i can display databus, address bus and i’ve been using this for address decoding logic and hex keyboard.
I’ve implemented a second VIA chip, and ordered components to amplify the SID sound part
"If something is worth doing, it's worth overdoing."
