Category Archives: Retrochallenge

RC2017/4: Introducing Arudino6502

This weekend I polished up my Arduino Day project and published it to GitHub for Retrochallenge 2017/04.

Introducing Arduino6502

The repository contains an Arduino sketch that can be loaded on Arduino Mega boards (Arduino Uno’s can be accommodated by lowering the RAMSIZE value).

The sketch includes ROM images for AppleSoft Lite and Krusader symbolic assembler.

To run AppleSoft BASIC, enter


And you will be dropped into the BASIC prompt


Remember that the Apple 1 was an upper case only machine, so you should enter all letters in upper case.

Krusader is available at $F000


What’s next?

The project currently targets the 8 bit Atmel chips due to the tight coupling between the Atmega 2560’s hardware serial port and the simulated 6821 PIA. The mapping is good enough that, as long as you insert a delay of 200ms or greater between newlines, you can paste HEX files into the Woz monitor and run the resulting program.

However, while the Apple 1 came with 4k or 8k of RAM, modern recreations like the Replica 1 assume at least 32k of RAM, making most of the software written for these nouveau Apple 1’s out of reach of this project.

To overcome this my next effort will be to port the project to run on Cortex-M platforms like the Teensy 3.x or Arduino Due to get access to more SRAM.

Retrochallenge 2017/04: 6502 on Arduino

This is my late entry for the 2017/04 retrochallenge. Notwithstanding my 2015 failure to launch, I plan to work on Arduino based emulators for various 6502 computers.

A few years ago I built an Arduino shield to host a real 6502 using the Arduino as RAM, PIA, and  glue logic. To some extent the software that this project ran was an afterthought, as it turned out the Apple 1 Woz monitor was perfect a proof of concept.

For the recent Arduino Day I brushed off my old code and reworked it to use an emulated CPU core so the sketch can run on an unadorned Arduino Uno or Mega.

For retrochallenge 2017/04 I plan to continue this work.


  • Clean up my sketch and publish the code to GitHub. I plan to target the Arduino Uno and Arduino Mega natively.
  • Hopefully add support for other monitors like Microsoft 8k BASIC.
  • Stretch goal: Rockwell made a 6502 variant called the R65F11 which was a 6502 with FORTH built into on chip ROM. Details are sketchy, but I found this pdf online and maybe if the ROM can be uncovered I can emulate that system.

Retrochallenge 2015/01 entry, reviving an Apple II motherboard

After lurking on the fringes of the hobbyist electronic and retrocomputing communities for a few years I’ve decided to take the plunge and join the RC2015/01 retrochallenge.

Apple II rev 7 motherboard circa '81

Apple II rev 7 motherboard circa ’81

The task I have assigned myself is to revive this 1981 vintage revision 7 Apple II motherboard which I discovered in a box of parts while visiting my family last week. I have a vague memory that I got this board and some other spare parts in the mid 90’s, but beyond that its origin is a mystery.

Off by one error

Off by one error

I have not tried to power up the board, but strongly suspect that it does not — if you look closely you can see that some wag has replaced the MOS 6502 with an Intersil 6402 UART! Astute readers will also note that not only are the ROMs out of order, but one is upside down.

This isn't the socket you are looking for

This isn’t the socket you are looking for

Clearly I’ll have my work cut out for me as I cannot assume anything on the board is working, or correct. There are also some minor repairs needed to the board (a transistor has snapped off, bent pins, covered in dirt, etc), but nothing that looks too scary.

So, in preparation for next January, it’s off to eBay to stockpile parts for test rigs and spares.