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PETSCII

PETSCII (shifted and unshifted)
Language	English withpseudographics
Classification	8-bit extended early ASCII
Based on	US-ASCII (1963 version)

PETSCII (PET Standard Code of Information Interchange), also known asCBM ASCII, is thecharacter set used inCommodore Business Machines' 8-bithome computers.

This character set was first used by thePET from 1977, and was subsequently used by theCBM-II,VIC-20,Commodore 64,Commodore 16,Commodore 116,Plus/4, andCommodore 128. However, theAmiga personal computer family instead uses standardISO/IEC 8859-1.

The character set was largely designed byLeonard Tramiel (the son of Commodore CEOJack Tramiel) and PET designerChuck Peddle.^[1][2][3] The graphic characters of PETSCII were one of the extensions Commodore specified forCommodore BASIC when laying out desired changes to Microsoft's existing6502BASIC to Microsoft'sRic Weiland in 1977.^[4] The VIC-20 used the same pixel-for-pixelfont as the PET, although the characters appeared wider due to the VIC's 22-column screen. The Commodore 64, however, used a slightly re-designed, heavy upper-case font, essentially a thicker version of the PET's, in order to avoidcolor artifacts created by the machine's higher resolution screen. The C64'slowercase characters are identical to the lowercase characters in theAtari 8-bit computers font (released 2.75 years earlier).

Peddle claims the inclusion ofcard suit symbols was spurred by the demand that it should be easy to write card games on the PET (as part of the specification list he received).^[2]

"Unshifted" PETSCII is based on the 1963 version ofASCII (rather than the 1967 version, which most if not all other computer character sets based on ASCII use). It has onlyuppercase letters, an up-arrow⟨↑⟩ instead ofcaret⟨^⟩ at0x5E and a left-arrow⟨←⟩ instead of anunderscore⟨_⟩ at 0x5F. In all versions except the original Commodore PET, it also has aBritish pound sign⟨£⟩ instead of the backslash⟨\⟩ at 0x5C. Other characters added in ASCII-1967 (lowercase letters, thegrave accent,curly braces, vertical bar, and tilde) do not exist in PETSCII. Codes 0xA0–0xDF are allotted to CBM-specificblock graphics characters—horizontal and vertical lines, hatches, shades, triangles, circles andcard suits.

PETSCII also has a "shifted" mode (also called "business mode"), which changes the uppercase letters at 0x41–0x5A to lowercase, and changes the graphics at 0xC1–0xDA to uppercase letters. Upper- and lower-case are swapped from where ASCII has them. The mode is toggled by holding one of the SHIFT keys and then pressing and releasing theCommodore key. The shift can be done byPOKEing location 59468 with the value 14 to select the alternative set or 12 to revert to standard. On the Commodore 64, the sets are alternated by flipping bit 2 of the byte 53272. On some models of PET, this can also be achieved via special control codePRINT CHR$(14) which adjust the line spacing as well as changing the character set; the POKE method is still available and does not alter the line spacing.^[5]

Included in PETSCII arecursor and screen control codes, such as{HOME},{CLR},{RVS ON}, and{RVS OFF} (the latter two activating/deactivating reverse-video character display). The control codes appeared in program listings as reverse-video graphic characters, although some computer magazines, in their efforts to provide more clearly readable listings,pretty-printed the codes using their actual names in curly braces, like the above examples. This is unambiguous as PETSCII has no curly brace characters.

Different mappings are used for storing characters (the "interchange" mapping, as used byCHR$()) and displaying characters (the "video" mapping). For example, to display the characters "@ABC" on screen by directly writing into thescreen memory, one would POKE the decimal values 0, 1, 2, and 3 rather than 64, 65, 66, and 67.^[6][7]

The keyboard by default provides access to the lower half of the code page. Pressing Shift and a key gives the corresponding upper half code point. Some PETSCII code points cannot be printed and are only used for keyboard input (e.g. F1, RUN/STOP).

This article contains uncommonUnicode characters. Without properrendering support, you may seequestion marks, boxes, or other symbols instead of the intended characters.

The tables below represent the "interchange" PETSCII encoding, as used byCHR$().

Control characters are defined in the ranges 0x00–0x1F and 0x80–0x9F, although which control characters are defined and what they are defined as varies between systems. The tables below exclude control characters—the encoding of control characters in discussed in§ Control characters.

The ranges 0x60–0x7F and 0xE0–0xFF are duplicate ranges, although what they duplicate varies between systems. On the Commodore PET, they duplicate 0x20–0x3F and 0xA0–0xBF, respectively; on the Commodore VIC-20, 64, 16, and 128 they duplicate 0xC0–0xDF and 0xA0–0xBF, respectively.^[6] While these characters are visually duplicates, they are semantically different; for example, on the Commodore PET, code points 0x2C and 0x6C both produce a comma character, but only 0x2C functions as a delimiter between input fields.^[8]

Graphic characters are mostly identical across systems, with the exceptions of 0x5C (which is\ on the Commodore PET, and£ on other systems), 0xDE (which is U+1FB95 CHECKER BOARD FILL on the Commodore PET and VIC-20, and U+1FB96 INVERSE CHECKER BOARD FILL on other systems), and the range 0x60–0x7F (which duplicates a different range on Commodore PET). Additionally, inCommodore PET 2001's shifted character set, uppercase and lowercase letters are swapped relative to other systems'.

PETSCII characters are represented in theUnicode standard in various blocks:

• Basic Latin (U+0000 - U+007F)
• Latin-1 Supplement (U+0080 - U+00FF)
• Greek and Coptic (U+03C0 πGREEK SMALL LETTER PI)
• General Punctuation (U+2022 •BULLET)
• Arrows (two arrows, U+2190 and U+2191)
• Box Drawing (U+2500 - U+257F)
• Block Elements (U+2580 - U+259F)
• Geometric Shapes (U+25A0 - U+25FF)
• Miscellaneous Symbols (U+2600 - U+26FF)
• Dingbats (U+2713 ✓CHECK MARK)
• Symbols for Legacy Computing (U+1FB00 - U+1FBFF, first added in 2020 as part of Unicode 13.0)^[9]

The following tables represent the PETSCII encoding used on the Commodore VIC-20, 64, 16, and 128.

While the graphic characters were mostly shared between Commodore systems, the control characters frequently varied. The follow table describes what the control characters represent on theCommodore PET 2001,Commodore PET 8032,VIC-20,Commodore 64,Commodore 16,Commodore 128 (40 and 80 column modes).

The colors of the VIC-20 and C64/128 are listed in theVIC-II article.

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Out of PETSCII's first 192 codes, there are 128 graphic characters: 32–127 and 160–192. This permits "base128"-style encodings in DATA statements, or perhaps between PETSCII-speaking machines. This can also include control characters, which are visible when quoted, although which control characters are defined varies between systems.

The primary application for a "Base 128" encoding is in DATA statements in Commodore BASIC. Binary data can be stored with relatively low overhead, allowing one character of data to encode seven bits of data. On a standard 80-character line, typically four characters are used for the line number, and two characters for the abbreviated DATA statement (dA). Since the comma and colon are significant to BASIC, a quote character is also needed, leaving 73 characters for data. At seven bits per character, one DATA line could store 511 bits of binary data, for 79% efficiency. If three-digit line numbers are used, efficiency increases to 80%. If two-digit line numbers are used, efficiency is 82%.

For storing binary data in Commodore BASIC, it appears that two- or three-digit line numbers are typically the best choice.

164 PETSCII characters are representable in quoted strings; theoretically, then, Base 164 is possible. This adds in the color values, the function keys, and cursor controls.

• ATASCII
• Atari ST character set
• ZX Spectrum character set
• Extended ASCII
• Text semigraphics

• PETSCII to Unicode mapping and aTrueType font using that mapping
• Typography in 8 bits: System fonts
• Online PETSCII-art editor
• PETSCII-art

• Character sets
• Commodore International
• Commodore 64
• VIC-20
• ASCII
• Computer-related introductions in 1977

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