{"id":46,"date":"2008-10-20T22:27:15","date_gmt":"2008-10-21T06:27:15","guid":{"rendered":"http:\/\/www.pagetable.com\/?p=46"},"modified":"2008-10-20T22:27:15","modified_gmt":"2008-10-21T06:27:15","slug":"create-your-own-version-of-microsoft-basic-for-6502","status":"publish","type":"post","link":"https:\/\/www.pagetable.com\/?p=46","title":{"rendered":"Create your own Version of Microsoft BASIC for 6502"},"content":{"rendered":"

Update<\/i>: The source is available at github.com\/mist64\/msbasic<\/a><\/p>\n

If you disassemble a single binary, you can never tell why something was done in a certain way. If you have eight different versions, you can tell a lot. This episode of “Computer Archeology<\/a>” is about reverse engineering eight different versions of Microsoft BASIC 6502 (Commodore, AppleSoft etc.), reconstructing the family tree, and understanding when bugs were fixed and when new bugs, features and easter eggs were introduced.<\/p>\n

This article also presents a set of assembly source files that can be made to compile into a byte exact copy of seven different versions of Microsoft BASIC, and lets you even create your own version.<\/a><\/p>\n

Microsoft BASIC for MOS 6502<\/h3>\n

First written in 1976, Microsoft BASIC for the 8 bit MOS 6502 has been available for virtually every 6502-based computer including the Commodore series (PET, C64), the Apple II series, Atari 8 bit machines, and many more.<\/p>\n

These are the first eight versions of Microsoft BASIC:<\/p>\n\n\n\n\n\n\n\n\n\n
Name<\/td>\nRelease<\/td>\nVER<\/td>\nROM<\/td>\nFP<\/td>\nROR<\/td>\nBuffer<\/td>\nExtensions<\/td>\nVersion<\/td>\n<\/tr>\n
Commodore BASIC 1<\/td>\n1977<\/td>\n<\/td>\nY<\/td>\n9<\/td>\nY<\/td>\nZP<\/td>\nCBM<\/td>\n1.0<\/td>\n<\/tr>\n
OSI BASIC<\/td>\n1977<\/td>\n1.0rev3.2<\/td>\nY<\/td>\n6<\/td>\nY<\/td>\n<\/td>\n–<\/td>\n1.0a<\/td>\n<\/tr>\n
AppleSoft I<\/td>\n1977<\/td>\n1.1<\/td>\nN<\/td>\n9<\/td>\nY<\/td>\n0200<\/td>\nApple<\/td>\n1.1<\/td>\n<\/tr>\n
KIM BASIC<\/td>\n1977<\/td>\n1.1<\/td>\nN<\/td>\n9<\/td>\nN<\/td>\nZP<\/td>\n–<\/td>\n1.1a<\/td>\n<\/tr>\n
AppleSoft II<\/td>\n1978<\/td>\n<\/td>\nY<\/td>\n9<\/td>\nY<\/td>\n0200<\/td>\nApple<\/td>\n2<\/td>\n<\/tr>\n
Commodore BASIC 2<\/td>\n1979<\/td>\n<\/td>\nY<\/td>\n9<\/td>\nY<\/td>\n0200<\/td>\nCBM<\/td>\n2a<\/td>\n<\/tr>\nKBD BASIC<\/td>\n1982<\/td>\n<\/td>\nY<\/td>\n6<\/td>\nY<\/td>\n0700<\/td>\nKBD<\/td>\n2b<\/td>\n<\/tr>\n
MicroTAN<\/td>\n1980<\/td>\n<\/td>\nY<\/td>\n9<\/td>\nN<\/td>\nZP<\/td>\n–<\/td>\n2c<\/td>\n<\/tr>\n<\/table>\n

Name<\/b>: Name of the computer system or BASIC interpreter<\/p>\n

Release<\/b>: Release date of this version – not necessarily the date when the source code was forked from Microsoft’s<\/p>\n

VER<\/b>: Version string inside the interpreter itself<\/p>\n

ROM<\/b>: Whether the software shipped in ROM, or was a program supposed to be loaded into RAM<\/p>\n

FP<\/b>: Whether the 6 digit or 9 digit floating point library was included. 9 digit als means that long error messages were included instead of two character codes, and the GET statement was supported.<\/p>\n

ROR<\/b>: Whether the ROR assembly instruction was used or whether the code worked around it<\/a><\/p>\n

Buffer<\/b>: Location of the direct mode input buffer; either zero page or above<\/p>\n

Extensions<\/b>: What BASIC extensions were added by the OEM, of any.<\/p>\n

Version<\/b>: My private version number used in this article and in my combined source<\/p>\n

The Microsoft BASIC 6502 Combined Source Code<\/h3>\n

Download the assembly source code here: msbasic.zip<\/a><\/p>\n

In order to assemble if, you will need the CC65<\/a> compiler\/assembler\/linker package.<\/p>\n

The source can be assembled into byte-exact versions of the following seven BASICs:<\/p>\n