Assembler and simulator for the 6502 processor
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Update: 9 April 2014

At the suggestion of Ed Spittles, I've pulled in some tests from Klaus Dormann. Specifically, I've copied his 6502_functional_test binary and listing to my bin/ directory here.

To run this test, there's a loader, klaus_dormann_test.rb, which loads the binary into memory and runs it until it detects a jmp * loop (jump to the current PC).

At this time, it's stopping at location 0x5eb, which, after referencing the code listing, tells me the stack pointer is not the correct value at that point. Todo: figure out why...

Update: 14 November 2012

It works. See my blog post

It probably bears no resemblance to the JS code which inspired the project, so don't get confused by that.

Also, the code (and especially the specs) need cleanup and refactoring, so don't judge. :)

Original intro:

Work-in-progress assembler and simulator of the 6502, written in Ruby.

Originally, I was going to fork Nick Morgan's JS simulation (, but I decided to do a rewrite in Ruby. (He's got a very nice interactive "book" on 6502 assembly programming.)

Nick's version is a modification of the excellent original, by Stian Soreng (, so probably the most thanks for the code goes to him.

I'm using the JS code as reference, but probably most of the internal structure will be quite different.

MIT Licensed