mattiasljungstrom / petscii8

PETSCII-8 is an 8-bit encoding with the goal of being compatible with both ASCII and PETSCII.

PETSCII-8

PETSCII-8 is an 8-bit encoding with the goal of being compatible with both ASCII and PETSCII.

Mapping from PETSCII to PETSCII-8

Mapping from PETSCII to PETSCII-8 is reasonably simple. Start with the following substitutions:

• Map 60 — 7F to C0 — DF (ADD 60 or XOR A0)
• Map E0 — FE to A0 — BE (SUB 40 or XOR 40)
• Map FF to DE
• Map 5C to E3
• Map 5E to ED
• Map 5F to EC

If in uppercase mode, we are done; no additional substitutions need to be made.

If in lowercase mode, the following additional substitutions need to be made following and on top of the previous ones:

• Map 41 — 5A to 61 — 7A (ADD 20 or XOR 20)
• Map C1 — DA to 41 — 5A (SUB 80 or XOR 80)
• Map A9 to E9
• Map BA to FA
• Map DE to either E8 (for compatibility with the PET or VIC-20) or FE (for compatibility with the C64 or C128)
• Map DF to FF

Mapping from PETSCII-8 to Unicode

A mapping table in Format A is included in MAPPINGS/PETSCII8.TXT.

00 — A0 map directly to U+0000 — U+00A0. The mapping for A0 — DF follows below. The mapping for E0 — FF is given in the Rationale section.

PETSCII-8	Unicode
A0	U+00A0 NO-BREAK SPACE
A1	U+258C LEFT HALF BLOCK
A2	U+2584 LOWER HALF BLOCK
A3	U+2594 UPPER ONE EIGHTH BLOCK
A4	U+2581 LOWER ONE EIGHTH BLOCK
A5	U+258F LEFT ONE EIGHTH BLOCK
A6	U+2592 MEDIUM SHADE
A7	U+2595 RIGHT ONE EIGHTH BLOCK
A8	U+1FB8F LOWER HALF MEDIUM SHADE
A9	U+25E4 BLACK UPPER LEFT TRIANGLE
AA	U+1FB87 RIGHT ONE QUARTER BLOCK
AB	U+251C BOX DRAWINGS LIGHT VERTICAL AND RIGHT
AC	U+2597 QUADRANT LOWER RIGHT
AD	U+2514 BOX DRAWINGS LIGHT UP AND RIGHT
AE	U+2510 BOX DRAWINGS LIGHT DOWN AND LEFT
AF	U+2582 LOWER ONE QUARTER BLOCK
B0	U+250C BOX DRAWINGS LIGHT DOWN AND RIGHT
B1	U+2534 BOX DRAWINGS LIGHT UP AND HORIZONTAL
B2	U+252C BOX DRAWINGS LIGHT DOWN AND HORIZONTAL
B3	U+2524 BOX DRAWINGS LIGHT VERTICAL AND LEFT
B4	U+258E LEFT ONE QUARTER BLOCK
B5	U+258D LEFT THREE EIGHTHS BLOCK
B6	U+1FB88 RIGHT THREE EIGHTHS BLOCK
B7	U+1FB82 UPPER ONE QUARTER BLOCK
B8	U+1FB83 UPPER THREE EIGHTHS BLOCK
B9	U+2583 LOWER THREE EIGHTHS BLOCK
BA	U+1FB7F RIGHT AND LOWER ONE EIGHTH BLOCK
BB	U+2596 QUADRANT LOWER LEFT
BC	U+259D QUADRANT UPPER RIGHT
BD	U+2518 BOX DRAWINGS LIGHT UP AND LEFT
BE	U+2598 QUADRANT UPPER LEFT
BF	U+259A QUADRANT UPPER LEFT AND LOWER RIGHT
C0	U+2500 BOX DRAWINGS LIGHT HORIZONTAL
C1	U+2660 BLACK SPADE SUIT
C2	U+1FB72 VERTICAL ONE EIGHTH BLOCK-4
C3	U+1FB78 HORIZONTAL ONE EIGHTH BLOCK-4
C4	U+1FB77 HORIZONTAL ONE EIGHTH BLOCK-3
C5	U+1FB76 HORIZONTAL ONE EIGHTH BLOCK-2
C6	U+1FB7A HORIZONTAL ONE EIGHTH BLOCK-6
C7	U+1FB71 VERTICAL ONE EIGHTH BLOCK-3
C8	U+1FB74 VERTICAL ONE EIGHTH BLOCK-6
C9	U+256E BOX DRAWINGS LIGHT ARC DOWN AND LEFT
CA	U+2570 BOX DRAWINGS LIGHT ARC UP AND RIGHT
CB	U+256F BOX DRAWINGS LIGHT ARC UP AND LEFT
CC	U+1FB7C LEFT AND LOWER ONE EIGHTH BLOCK
CD	U+2572 BOX DRAWINGS LIGHT DIAGONAL UPPER LEFT TO LOWER RIGHT
CE	U+2571 BOX DRAWINGS LIGHT DIAGONAL UPPER RIGHT TO LOWER LEFT
CF	U+1FB7D LEFT AND UPPER ONE EIGHTH BLOCK
D0	U+1FB7E RIGHT AND UPPER ONE EIGHTH BLOCK
D1	U+25CF BLACK CIRCLE
D2	U+1FB7B HORIZONTAL ONE EIGHTH BLOCK-7
D3	U+2665 BLACK HEART SUIT
D4	U+1FB70 VERTICAL ONE EIGHTH BLOCK-2
D5	U+256D BOX DRAWINGS LIGHT ARC DOWN AND RIGHT
D6	U+2573 BOX DRAWINGS LIGHT DIAGONAL CROSS
D7	U+25CB WHITE CIRCLE
D8	U+2663 BLACK CLUB SUIT
D9	U+1FB75 VERTICAL ONE EIGHTH BLOCK-7
DA	U+2666 BLACK DIAMOND SUIT
DB	U+253C BOX DRAWINGS LIGHT VERTICAL AND HORIZONTAL
DC	U+1FB8C LEFT HALF MEDIUM SHADE
DD	U+2502 BOX DRAWINGS LIGHT VERTICAL
DE	U+03C0 GREEK SMALL LETTER PI
DF	U+25E5 BLACK UPPER RIGHT TRIANGLE

Rationale

Each and every character and its placement in PETSCII-8 is chosen carefully and deliberately:

• Characters 00-7F are identical to ASCII.

• Characters 00-5F and 80-DF are identical to PETSCII with the exception of the characters £ ↑ ←, which have been relocated for sake of ASCII compatibility.

• Characters E0-FF include PETSCII characters which map to multiple Unicode characters (for round-trip compatibility), characters from the lowercase mode of PETSCII, and a selection of characters from the Teletext G2 character set and ISO Latin-9:

PETSCII-8	Unicode	Rationale
E0	U+1FB79 HORIZONTAL ONE EIGHTH BLOCK-5	C0 in PETSCII. Also mappable to U+2500 BOX DRAWINGS LIGHT HORIZONTAL, but we use C0 for the version mapped to that character.
E1	U+00A1 INVERTED EXCLAMATION MARK	A1 in Teletext G2 and ISO Latin-9, hence the encoding at E1.
E2	U+00A2 CENT SIGN	A2 in Teletext G2 and ISO Latin-9, hence the encoding at E2.
E3	U+00A3 POUND SIGN	5C in PETSCII, but relocated for sake of ASCII compatibility. A3 in Teletext G2 and ISO Latin-9, hence the encoding at E3.
E4	U+20AC EURO SIGN	A4 in ISO Latin-9, hence the encoding at E4.
E5	U+00A5 YEN SIGN	A5 in Teletext G2 and ISO Latin-9, hence the encoding at E5.
E6	U+2022 BULLET	D1 in PETSCII. Also mappable to U+25CF BLACK CIRCLE, but we use D1 for the version mapped to that character.
E7	U+00A7 SECTION SIGN	A7 in Teletext G2 and ISO Latin-9, hence the encoding at E7.
E8	U+1FB95 CHECKER BOARD FILL	DE in PETSCII lowercase mode on the Commodore PET and VIC-20. Can't be FE in PETSCII-8 due to collision with INVERSE CHECKER BOARD FILL.
E9	U+1FB99 UPPER RIGHT TO LOWER LEFT FILL	A9 in PETSCII lowercase mode.
EA	U+25E6 WHITE BULLET	D7 in PETSCII. Also mappable to U+25CB WHITE CIRCLE, but we use D7 for the version mapped to that character.
EB	U+00AB LEFT-POINTING DOUBLE ANGLE QUOTATION MARK	AB in Teletext G2 and ISO Latin-9, hence the encoding at EB.
EC	U+2190 LEFTWARDS ARROW	5F in PETSCII, but relocated for sake of ASCII compatibility. AC in Teletext G2, hence the encoding at EC.
ED	U+2191 UPWARDS ARROW	5E in PETSCII, but relocated for sake of ASCII compatibility. AD in Teletext G2, hence the encoding at ED.
EE	U+2192 RIGHTWARDS ARROW	AE in Teletext G2, hence the encoding at EE.
EF	U+2193 DOWNWARDS ARROW	AF in Teletext G2, hence the encoding at EF.
F0	U+00B0 DEGREE SIGN	B0 in Teletext G2 and ISO Latin-9, hence the encoding at F0.
F1	U+00B1 PLUS-MINUS SIGN	B1 in Teletext G2 and ISO Latin-9, hence the encoding at F1.
F2	U+00AE REGISTERED SIGN	D2 in Teletext G2, hence the encoding at F2. Also AE in ISO Latin-9, but can't be EE in PETSCII-8 due to collision with RIGHTWARDS ARROW.
F3	U+00A9 COPYRIGHT SIGN	D3 in Teletext G2, hence the encoding at F3. Also A9 in ISO Latin-9, but can't be E9 in PETSCII-8 due to collision with UPPER RIGHT TO LOWER LEFT FILL.
F4	U+00D7 MULTIPLICATION SIGN	B4 in Teletext G2, hence the encoding at F4. Also D7 in ISO Latin-9, but can't be F7 in PETSCII-8 due to collision with MIDDLE DOT.
F5	U+00B5 MICRO SIGN	B5 in Teletext G2 and ISO Latin-9, hence the encoding at F5.
F6	U+00B6 PILCROW SIGN	B6 in Teletext G2 and ISO Latin-9, hence the encoding at F6.
F7	U+00B7 MIDDLE DOT	B7 in Teletext G2 and ISO Latin-9, hence the encoding at F7.
F8	U+00F7 DIVISION SIGN	B8 in Teletext G2, hence the encoding at F8. Also F7 in ISO Latin-9, but can't be F7 in PETSCII-8 due to collision with MIDDLE DOT.
F9	U+00BF INVERTED QUESTION MARK	BF in Teletext G2 and ISO Latin-9, but can't be FF in PETSCII-8 due to collision with UPPER LEFT TO LOWER RIGHT FILL.
FA	U+2713 CHECK MARK	BA in PETSCII lowercase mode.
FB	U+00BB RIGHT-POINTING DOUBLE ANGLE QUOTATION MARK	BB in Teletext G2 and ISO Latin-9, hence the encoding at FB.
FC	U+00AC NOT SIGN	AC in ISO Latin-9, but can't be EC in PETSCII-8 due to collision with LEFTWARDS ARROW.
FD	U+1FB73 VERTICAL ONE EIGHTH BLOCK-5	DD in PETSCII. Also mappable to U+2502 BOX DRAWINGS LIGHT VERTICAL, but we use DD for the version mapped to that character.
FE	U+1FB96 INVERSE CHECKER BOARD FILL	DE in PETSCII lowercase mode on the Commodore 64 and 128.
FF	U+1FB98 UPPER LEFT TO LOWER RIGHT FILL	DF in PETSCII lowercase mode.

The only non-alphabetic characters in ISO Latin-9 not in PETSCII-8 are ¹ ² ³ ª º ¯ and soft hyphen. Similarly, the only non-alphabetic characters in Teletext G2 not in PETSCII-8 are ¹ ² ³ ‘ ’ “ ” ¤ ™ ♪ ₠ ‰ α ¼ ½ ¾ ⅛ ⅜ ⅝ ⅞ ª º and diacritical marks. You can see that we're not missing much.