Bass 6502 Assembler

Bass is a macro assembler for 6502 cross-development written by Aleksi Eeben in 2025. Development is ongoing, with new features added as needed and bugs fixed as they are discovered. The latest update introduces memory banking, large REU export support, ROM image generation for game consoles, and optional 65C02 instruction set support.

Bass aims to be minimalistic, clutter-free, precise, and enjoyable to use, with minimal mental overhead from remembering directive syntax or unnecessary formalities. Just write code and sip coffee all night. If you’ve used DASM or ASM-One, you’ll feel at home.

Target platforms include: C64, VIC-20, C128, C16/Plus4, NES, Apple II/IIe/IIc, Atari 2600, Atari Lynx, Atari 400/800/5200/7800, Oric-1, Oric Atmos, Acorn Atom, Acorn Electron, BBC Micro, Acorn Master 128, Commander X16, PC Engine / TurboGrafx-16, and T-800 Model 101.

Bass is written in Lua, with precompiled binaries available for macOS, Windows, Linux PCs, and Raspberry Pi 5 (Pi 3/4 with 64-bit OS should also work). A Lua bytecode version is provided, built with Lua 5.4.8.

Version History

Version 1.02 (18 Nov 2025)

• Added memory banking
• Added exporting of large REU files
• Added ROM image generation for game consoles
• Added optional 65C02 mode
• New directives: bank, reusave, append

Version 1.01 (25 Sep 2025)

• Added one directive
• Added a few error checks
• Corrected a blocked variable name

Version 1.00 (20 Sep 2025)

• First public release

See the Bass Manual for detailed information:
https://sourceforge.net/projects/bass-6502-assembler/files/Bass%20Manual.pdf

Note

You may not use Bass to compile T-800 Model 101 code that could be harmful to humans.

License

Freeware. You may use and redistribute the original, unmodified files. Modification, reverse engineering, or other forms of creative exploration are not encouraged. Source code is not currently provided.

If you enjoy using Bass, feel free to support development via Ko-fi:
https://ko-fi.com/aleksieeben