/pet'skee/ PET ASCII. The variation (many would say perversion) of the ASCII character set used by the Commodore Business Machines' PET series of personal computers and the later Commodore 64, Commodore 16, and Commodore 128 computers. The PETSCII set used left-arrow and up-arrow (as in old-style ASCII) instead of underscore and caret, placed the unshifted alphabet at positions 65--90, put the shifted alphabet at positions 193--218, and added graphic characters.