Definition of the DEFINE instruction used in the source for Microsoft BASIC

Question

Does anyone know where I can find the definition of the DEFINE keyword/instruction used in the source code of the Microsoft BASIC interpreter released to the public by Microsoft here: https://github.com/microsoft/BASIC-M6502/blob/main/m6502.asm

As an example the source code contains:

DEFINE  LDXY    (WD),<
    LDX WD
    LDY <WD>+1>

This might mean the defined symbol LDXY with the parameter (WD) is replaced by the right hand side after the comma. The right hand side is enclosed in arrow-shaped bracket.

But I cannot find documentation on the DEFINE assembler instruction anywhere!

Thanks

Answer 1 · 2025-11-10 20:49:27Z

Michael Petch

• modified Nov 10 at 22:10

The code is using macros which are created with the DEFINE operator. I believe MS Basic for the 6502 was written with Macro-10 assembler. You can find the manual here: https://bitsavers.org/pdf/dec/pdp10/TOPS10/1973_Assembly_Language_Handbook/02_1973AsmRef_macro.pdf . Review page 259+ (Chapter 3) for the syntax of macro definitions.

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Definition of the DEFINE instruction used in the source for Microsoft BASIC

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