Computer

6502 Update

Last Updated or created 2022-09-14

New address decoder in place!
Connected RAM/ROM/SID/VIA1/VIA2 and ACIA

ROM8000-FFFF
SID7000-700F (sound)
VIA16000-60xx (Hex key matrix)
ACIA6800-68xx (serial)
VIA25000-50xx (led test at the moment)
RAM0000-3FFF

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