Microsoft BASIC for 6502

This is a single integrated assembly source tree that can generate nine different versions of Microsoft BASIC for 6502.

By running ./make.sh, this will generate all versions and compare them to the original files byte by byte. The CC65 compiler suite is need to build this project.

These are the first ten (known) versions of Microsoft BASIC for 6502:

Name	Release	MS Version	ROM	9digit	INPUTBUFFER	extensions	.define
Commodore BASIC 1	1977		Y	Y	ZP	CBM
OSI BASIC	1977	1.0 REV 3.2	Y	N	ZP	-	CONFIG_10A
AppleSoft I	1977	1.1	N	Y	$0200	Apple	CONFIG_11
KIM BASIC	1977	1.1	N	Y	ZP	-	CONFIG_11A
AppleSoft II	1978		Y	Y	$0200	Apple	CONFIG_2
AIM-65 BASIC	1978	1.1?	Y	N	ZP	AIM	CONFIG_2A
SYM-1 BASIC	1978	1.1?	Y	N	ZP	SYM	CONFIG_2A
Commodore BASIC 2	1979		Y	Y	$0200	CBM	CONFIG_2A
KBD BASIC	1982		Y	N	$0700	KBD	CONFIG_2B
MicroTAN	1980		Y	Y	ZP	-	CONFIG_2C

(Note that this assembly source cannot (yet) build AppleSoft II.)

This lists the versions in the order in which they were forked from the Microsoft source base. Commodore BASIC 1, as used on the original PET is the oldest known version of Microsoft BASIC for 6502. It contains some additions to Microsoft's version, like Commodore-style file I/O.

The CONFIG_n defines specify what Microsoft-version the OEM version is based on. If CONFIG_2B is defined, for example, CONFIG_2A, CONFIG_2, CONFIG_11A, CONFIG_11 and CONFIG_10A will be defined as well, and all bugfixes up to version 2B will be enabled.

The following symbols can be defined in addition:

Configuration Symbol	Description
CONFIG_CBM1_PATCHES	jump out into CBM1's binary patches instead of doing the right thing inline
CONFIG_CBM_ALL	add all Commodore-specific additions except file I/O
CONFIG_DATAFLG	?
CONFIG_EASTER_EGG	include the CBM2 "WAIT 6502" easter egg
CONFIG_FILE	support Commodore PRINT#, INPUT#, GET#, CMD
CONFIG_IO_MSB	all I/O has bit #7 set
CONFIG_MONCOUT_DESTROYS_Y	Y needs to be preserved when calling MONCOUT
CONFIG_NO_CR	terminal doesn't need explicit CRs on line ends
CONFIG_NO_LINE_EDITING	disable support for Microsoft-style "@", "_", BEL etc.
CONFIG_NO_POKE	don't support PEEK, POKE and WAIT
CONFIG_NO_READ_Y_IS_ZERO_HACK	don't do a very volatile trick that saves one byte
CONFIG_NULL	support for the NULL statement
CONFIG_PEEK_SAVE_LINNUM	preserve LINNUM on a PEEK
CONFIG_PRINTNULLS	whether PRINTNULLS does anything
CONFIG_PRINT_CR	print CR when line end reached
CONFIG_RAM	optimizations for RAM version of BASIC, only use on 1.x
CONFIG_ROR_WORKAROUND	use workaround for buggy 6502s from 1975/1976; not safe for CONFIG_SMALL!
CONFIG_SAFE_NAMENOTFOUND	check both bytes of the caller's address in NAMENOTFOUND
CONFIG_SCRTCH_ORDER	where in the init code to call SCRTCH
CONFIG_SMALL	use 6 digit FP instead of 9 digit, use 2 character error messages, don't have GET
CONFIG_SMALL_ERROR	use 2 character error messages

Changing symbol definitions can alter an existing base configuration, but it not guaranteed to assemble or work correctly.

More Information

More information on the differences of the respective versions can be found on this blog entry: Create your own Version of Microsoft BASIC for 6502.

Also, Ben Eater has an published excellent video demonstrating how to port BASIC to a new system: Running MSBASIC on my breadboard 6502 computer

License

2-clause BSD

Credits

• Main work by Michael Steil mist64@mac.com.
• AIM-65 and SYM-1 by Martin Hoffmann-Vetter
• Function names and all uppercase comments taken from Bob Sander-Cederlof's excellent AppleSoft II disassembly.
• Applesoft lite by Tom Greene helped a lot, too.
• Thanks to Joe Zbicak for help with Intellision Keyboard BASIC
• This work is dedicated to the memory of my dear hacking pal Michael "acidity" Kollmann.