Using petcat for cross-developing BASIC programs

The VICE emulator for Commodore computers includes a command-line tool called petcat that can convert between ASCII text files and Commodore BASIC PRG files. It is useful for writing BASIC programs on a modern computer in a text editor, among other things. While VICE does not yet include a MEGA65 emulator, the petcat tool does support creating and reading MEGA65 BASIC programs.

For example, you can write this temperature conversion program in an ASCII text file, like so:

100 print "enter a temperature in degrees fahrenheit:"
110 input f
120 c=(f-32)*5/9
130 print
140 print f;" degrees fahrenheit is ";c;" degrees celsius."

To convert this to a MEGA65 PRG file, use this command:

petcat -w65 -o tempconv.prg -- tempconv.bas

To convert a BASIC PRG back to text:

petcat -65 -o myprog.bas -- myprog.prg

petcat syntax

petcat text files are ASCII text. To fully represent all of the Commodore PETSCII characters that can appear in a BASIC program, including “quoted” control codes in strings, petcat uses a text-based syntax.

Letters, numbers, and punctuation common to both PETSCII and ASCII appear as ASCII. Letters are lowercase.

PETSCII	petcat	Notes

PETSCII	petcat	Notes
`A`	`a`
`1`	`1`
`+`	`+`

Several PETSCII-specific punctuation characters have similar codes as ASCII characters. These appear in petcat listings as their ASCII equivalents.

PETSCII	petcat	Notes

PETSCII	petcat	Notes
`£` (pound)	`\`	See exceptions below for Shift and Mega variants.
Left arrow	`_`
Up arrow	`^`
`π` (pi)	`~`

Graphics characters formed by pressing Shift and a letter are represented by uppercase letters.

PETSCII	petcat	Notes

PETSCII	petcat	Notes
Spade	`A`	Shift + A
Heart	`S`	Shift + S
Diamond	`Z`	Shift + Z
Club	`X`	Shift + X

All other PETSCII codes use a label syntax in petcat, surrounded by curly brackets: {...}

Shifted non-letter characters are labels with the prefix SHIFT-. A shifted pound spells out POUND.

PETSCII	petcat	Notes

PETSCII	petcat	Notes
Thick cross	`{SHIFT-+}`	Shift + `+`
Mid-bar	`{SHIFT-*}`	Shift + `*`
Upper-left triangle	`{SHIFT-POUND}`	Shift + `£`

All characters accessed by pressing Mega and a character key are labels with the prefix CBM-.

PETSCII	petcat	Notes

PETSCII	petcat	Notes
Upper-left corner	`{CBM-A}`	Mega + A
Upper-right corner	`{CBM-S}`	Mega + S
Half-checkerboard	`{CBM-POUND}`	Mega + `£`

The sixteen color control codes have labels similar to their keycap spellings.

PETSCII	petcat	Notes

PETSCII	petcat	Notes
Black	`{blk}`	Color 0; Ctrl + 1
White	`{wht}`	Color 1; Ctrl + 2
Red	`{red}`	Color 2; Ctrl + 3
Cyan	`{cyan}`	Color 3; Ctrl + 4
Purple	`{pur}`	Color 4; Ctrl + 5
Green	`{grn}`	Color 5; Ctrl + 6
Blue	`{blu}`	Color 6; Ctrl + 7
Yellow	`{yel}`	Color 7; Ctrl + 8
Orange	`{orng}`	Color 8; Mega + 1
Brown	`{brn}`	Color 9; Mega + 2
Light red	`{lred}`	Color 10; Mega + 3
Grey 1	`{gry1}`	Color 11; Mega + 4
Grey 2	`{gry2}`	Color 12; Mega + 5
Light green	`{lgrn}`	Color 13; Mega + 6
Light blue	`{lblu}`	Color 14; Mega + 7
Grey 3	`{gry3}`	Color 15; Mega + 8

Other control codes also have named labels. If a control code does not have a named label and can be typed with Ctrl plus a key, it is represented with a label with a CTRL- prefix.

PETSCII	petcat	Notes

PETSCII	petcat	Notes
Underline on	`{CTRL-B}`
Stop	`{stop}`
Bell	`{CTRL-G}`
Tab	`{CTRL-I}`
Linefeed	`{CTRL-J}`
Shift enable	`{ensh}`
Shift disable	`{dish}`
Switch to lowercase	`{swlc}`	Wikipedia’s PETSCII table calls this “text mode.”
Switch to uppercase	`{swuc}`	Wikipedia’s PETSCII table calls this “graphics.”
Flashing on	`{CTRL-O}`
Cursor down	`{down}`
Cursor up	`{up}`
Cursor left	`{left}`
Cursor right	`{rght}`
Reverse on	`{rvon}`	Ctrl + 9
Reverse off	`{rvoff}`	Ctrl + 0 (zero)
Home	`{home}`
Clear	`{clr}`	Shift + Home
Insert	`{inst}`	Shift + Del

These PETSCII codes cannot appear as characters in program listings or quoted strings. To include them in a BASIC string in a program, use the CHR$() function and string concatenation. Useful printable codes:

Return: CHR$(13)
Delete: CHR$(20)
Escape: CHR$(27)
Underline off: CHR$(130)
Flashing off: CHR$(143)

petcat source code

You can read the source code for petcat in the VICE source repository.