Computer

Composite video PCB working

Last Updated or created 2022-11-08

UPDATE 20221108

Soldered the components on the print
No more sync issues! (see post https://www.henriaanstoot.nl/2022/10/19/composite-video-with-atmega328p/ )

There are some duplicate characters, the input device below does not have a proper debounce method.

My temporary input device (note hex 21 is a “!” character)

No need to fix the debounce, the dipswitches are temporary. This will be controlled by the VIA 6522 chip.

UPDATE 20221108 (Connected to second VIA)

PORTB = $5000
PORTA = $5001
DDRB = $5002
DDRA = $5003
clock = $e0

E  = %10000000
RW = %01000000
RS = %00000000

  .org $0200

reset:
  ldx #$ff
  txs

  lda #%11111111 ; Set all pins on port B to output
  sta DDRB
  lda #%10000000 ; Set top pin on port A to output
  sta DDRA
  lda #$00  ; reset bit
  sta PORTA
  sta clock

  ldx #0
print:
  lda message,x
  beq printborder
  jsr print_char
  inx
  jmp print

loop:
  jmp loop

message:
        .db 0x01,0x04,0x0C,0x0E,0x10,0x0F,0x08
        .db 0x05,0x0a,0x0a
        .db 0x05,0x0b,0x0b
        .asc "Composite Video 6502 - 20221108"
        .db 0x0E,0x11,0x0F,0x0C
        .asciiz " With 2 pixels "

waitloop:
  pha
  tya
  pha
  ldy #$ff
back:
  dey
  bne back
  pla
  tay
  pla
  rts

print_char:
  sta PORTB
  jsr waitloop
  jsr waitloop
  lda clock
  eor #%10000000
  sta clock
  sta PORTA
  jsr waitloop
  lda clock
  eor #%10000000
  sta PORTA
  jsr waitloop
  rts

Control codes as from : http://searle.x10host.com/MonitorKeyboard/index.html

Video display control codes:
Hex (Decimal) and meaning
01 (01) - Cursor home (Standard ASCII)
02 (02) - Define cursor character (2nd byte is the curs character, or 00 to turn off) <--New for 3.0
03 (03) - Cursor blinking
04 (04) - Cursor solid
05 (05) - Set graphics pixel (next two bytes = x,y) <--New for 3.0
06 (06) - Reset graphics pixel (next two bytes = x,y) <--New for 3.0
08 (08) - Backspace (Standard ASCII)
09 (09) - Tab (Standard ASCII)
0A (11) - Linefeed (Standard ASCII)
0C (12) - Clear screen (Standard ASCII)
0D (13) - Carriage return (Standard ASCII)
0E (14) - Set column 0 to 79 (2nd byte is the column number) or 0 to 39 for a 40 char line
0F (16) - Set row 0 to 24 (2nd byte is the row number)
10 (16) - Delete start of line
11 (17) - Delete to end of line
12 (18) - Delete to start of screen
13 (19) - Delete to end of screen
14 (20) - Scroll up
15 (21) - Scroll down
16 (22) - Scroll left
17 (23) - Scroll right
18 (24) - Set font attribute for the current line (see elsewhere on this page for details) <--New for 3.0
1A (26) - Treat next byte as a character (to allow PC DOS char codes 1 to 31 to be displayed on screen)
1B (27) - ESC - reserved for ANSI sequences
1C (28) - Cursor right
1D (29) - Cursor Left
1E (30) - Cursor up
1F (31) - Cursor down
20 (32) to 7E (126) - Standard ASCII codes
7F (127) - Delete
80 (128) to FF (255) - PC (DOS) extended characters