Microsoft BASIC for the Picocomputer 6502

• INSTALL basic.rp6502 then HELP basic for usage.
• INFO basic.rp6502 for usage without installing.

Original source: https://github.com/microsoft/BASIC-M6502
Ported to cc65: https://github.com/mist64/msbasic

Launch arguments

basic [-c0|-c1|-c2] [<filename>]

Flag	Effect
-c0	Caps mode off — characters echo as typed
-c1	Caps mode on (default) — letters always upper case
-c2	Caps mode invert — swap upper/lower case
<name>	Auto-LOAD the file, then RUN it

The same modes are reachable at runtime via CAPS <expr>.

File I/O

Up to sixteen files may be open at once. Logical file numbers (lfn) are integers in the range 0..15.

OPEN <lfn>, <name$> [, <mode$>]
CLOSE <lfn>

<mode$> is a Unix-style string. If omitted, the default is "r".

Mode	Flags
"r"	read-only (default)
"w"	write, create, truncate
"a"	write, create, append
"rw" / "r+"	read/write
"w+"	read/write, create, truncate
"a+"	read/write, create, append

Once a file is open, the lfn drives I/O redirection on CBM-style statements:

PRINT# <lfn>, <expr-list>      : write to the file
INPUT# <lfn>, <var-list>       : read from the file (newline-delimited)
GET#   <lfn>, <var>            : read one byte from the file
CMD    <lfn> [, <expr-list>]   : redirect subsequent PRINT output

Reads return EOF when the OS returns fewer bytes than requested. INPUT# then bails cleanly to the caller; GET# simply returns an empty value, so polling a pipe in BASIC is a normal GET# loop.

LOAD and SAVE operate on plain ASCII — the same byte stream LIST emits — so program files are interchangeable with anything that produces text:

SAVE "prog.bas"
LOAD "prog.bas"

SAVE always overwrites; LOAD replaces the program in memory.

Other statements

CAPS <expr>

Sets the readline editor's caps mode at runtime: 0 off, 1 on, 2 invert. Same modes as the -c<n> launch flag. Anything else raises ?ILLEGAL QUANTITY.

Editor and runtime conveniences

• CTRL-C interrupts a running program or LIST.
• Type a line number then press TAB to recall that line into the editor for in-place editing.
• Keywords and variable names may be entered in lower case; they are normalized for tokenization and listing.
• RND() is seeded with hardware entropy at cold start, so RND produces a different sequence on each boot without needing a manual seed.
• CTRL-ALT-DEL (or BREAK) drops to the RP6502 monitor — useful for listing/changing directories or managing files. Type RESET at the monitor prompt to warm-start the interpreter while preserving program memory.