The five assemblers used by Commodore for their computers #Commodore #Programming #VintageComputing @pagetable

Michael Steil documents the five 6502 assemblers used by Commodore between 1975 and 1989:

Commodore used 5 different assemblers, most of them in-house tools, to build the ROMs for their Computers like the PET, the C64 and the C128. Nevertheless, all Commodore source files, from 1975 to 1990, share a common format and use the same assembly directives. This series of articles describes each of these assemblers.

In late 1975, MOS Technology, Inc. introduced the 6502 CPU and in 1976, they released the KIM-1, a demonstration/development platform for the 6502. Commodore bought MOS in November 1976, and the 6502 and the KIM-1 became Commodore products.

MOS also developed two assemblers for the 6502:

  • The “Cross-Assembler” (1975), available for various mainframes and minicomputers.
  • The “Resident Assembler” (1976), running on 6502 systems. It was ported to all Commodore 8-bit computers. The C64 version was sold as the “C64 Macro Assembler” in 1982.

Both assemblers were compatible in that they understood the same source format, with the same math features and the same directives and options.

There is a series of articles covering all the assemblers used:

See the introduction in the post here.

If you are interested in Commodore’s source code, see the GitHub repo here.


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