Tag Archives: RC2017/04

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.