6502 progress

Last Updated or created 2023-02-02

UPDATE: 20220815, 20220814, 20220815, 20230202

Flashing ROMs .. (eeproms). It used to be a pain in the *$$.
Burning took a looong time. But clearing one with UV took .. 20 minutes or so. Using one of these:

Altered clock module

  • Changed button press
  • Dipswitches for more speed control (red .. upper left)

Changed Rom/Ram

  • Changed addressing
  • Added RAM
  • ZIF Socket for ROM

VIC 6522

  • Fixed clock
  • Added buttons for interrupt


  • Display works now
  • To test: Create Address logic to access display without VIA
    Can work, but not at high speed clock. Stays behind VIA
  • To buy: st7920 lcd 128×64

Generic improvements

  • Rewired most parts, using color codes
    (Blue data, Yellow Address and so on)
  • Added leds on data and address bus using ULN2803 darlington arrays
  • 100nF Decoupling capacitors on the power rails

To do’s or ‘have to look into’s’

  • For sound i planned to use a General Instrument AY-3-8910, it is somewhere in my Lab, i know it is.
    I saved this chip and a SID for my Amiga addon soundcard.
    Where are my plans for the simple v1 setup? (FOUND IT)

  • I have to start writing rom functions for display usage. Like
    JSR $ff00 – Clear screen subroutine .. etc
  • I’m scraping information from websites, to get started on my clock controller.
    ATmega328 with ssd1306 display and rotary encoder/dip switches

Notes about the movie:
Left side is Arduino IDE monitor reading Addressbus and Databus.
(I’m going to try to rewrite this to realtime disassemble)
Resetting system.
Stepping CPU with manual clock pulses.
Start vector being read at $FFFC/$FFFD.
Program being run from $8000.
Set clock on automatic ( ~ about 150 Hz )
Last opcodes you see a JMP loop 4C 2F 80, that is JMP $802F
Display enlarged on video, was not visible on movie i took on mobile.
(Wrong angle?)

Breadboard overview

Clock moduleReset module + Crystal
CPU + nmi/int buttonsRAM and ROM
Address decode + Bus divideAddres/Data bus leds
6522 VIA + Display2nd via + Buttons
?(sound board)

TIL: 6502 can run without ram only rom,expect when using JSR … which uses a program stack in RAM


  • Make Clock module and 1Mhz Crystal switchable
  • NMI and INT debounce maken
  • Software buttons
  • Buy new darlingtons, for controlbus!
    • r/w, int, chip enables, etc
  • Labels on chips/breadboards
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