C64 character encoding

The commodore 64 has two character encoding schemes; Petscii and screencode. Petscii is what you use when you print using the standard $ffd2 charout print routine and screencodes is what you use when you poke the values directly to the screen.

In addition to this, you can toggle between upper/lower and upper/gfx by pressing Commodore + Shift

Printing $8e will take you to upper/gfx and printing $0e will take you to lower. You can block this by printing $08 and you can enable it again using $09.

Simple enough, and most of the times it is apparent if it’s done right as it will show up on the screen. However, one distinguishable difference is if you work with the drive. Filenames and disk commands must be in the proper format, or it won’t work. After AGAIN spending hours in a ghost chasing bug hunt, which was caused by setting a string to petscii upper/lower I got fed up and decided to have this blog post for my own reference. 🙂

Code:

	*=$1000


.encoding "screencode_mixed" 	//default

smix:	.text "abcdefgh"
	.text "ABCDEFGH"


.encoding "screencode_upper"

supper:	.text "abcdefgh"
	.text "ABCDEFGH"

.encoding "petscii_mixed"


pmix:	.text "abcdefgh"
	.text "ABCDEFGH"


.encoding "petscii_upper"

pupper:	.text "abcdefgh"
	.text "ABCDEFGH"


/* Result:

>C:1000  01 02 03 04  05 06 07 08   ........
>C:1008  41 42 43 44  45 46 47 48   ABCDEFGH

>C:1010  61 62 63 64  65 66 67 68   abcdefgh
>C:1018  01 02 03 04  05 06 07 08   ........

>C:1020  41 42 43 44  45 46 47 48   ABCDEFGH
>C:1028  c1 c2 c3 c4  c5 c6 c7 c8   ........

>C:1030  61 62 63 64  65 66 67 68   abcdefgh
>C:1038  41 42 43 44  45 46 47 48   ABCDEFGH

If using Screencode_mixed, disk commands and filenames should be in UPPER CASE.
If using petscii_mixed, disk commands and filenames should be in lower case.
*/