The numbers that computers and printers use are in binary form, which means they use only digits 0 and 1. In this manual, however, we use decimal num hers in our explanations because most users are more familiar with these numbers and because most programming languages and applications programs can use decimal numbers. The computer sys- tem or the program takes care of changing the decimal numbers to binary form. Computer and printer interaction would be confusing if different kinds of computers and printers used different numbers for the same letter of the alphabet.
Therefore, most manufacturers of computers, printers, and software use the American Standard Code for Information Interchange usually referred to as ASCII. ASCII covers the decimal numbers from 0 through 127 and includes codes for characters (letters, punctuation, numerals and mathematical symbols) and a few control codes, such as codes for sounding the beeper and performing a carriage return. Since ASCII codes run only from 1 to 127, there are extended versions of ASCII systems that feature additional characters and control codes.
The two extended versions that you may make use of with this printer, PETASCII (the Commodore version of ASCII) and IBM Character Graphics Set ASCII, are different from standard ASCII. In Commodore mode, a special extended version of the standard ASCII system is used. This code system is known as PETASCII (named for the first Commodore computer, the PET) or as Commodore ASCII. PETASCII is divided into two code tables, one for uppercase/ graphic mode and one for lowercase/uppercase mode. Control code characters are from 0 to 31, and numbers and punctuation character codes (32-63) receive the same codes as in standard ASCII, bur the remaining codes differ in PETASCII.
One major difference in PETASCII is that lowercase characters occupy codes 64-95 instead of uppercase (as in standard ASCII). Uppercase characters in PETASCII are from 192-223, rather than from 96-127 of standard ASCII. The PETASCII codes that can be entered from the keyboard are 0-95 and 160-223. Codes 96-127 are the same as codes 192-223, but cannot be entered from the keyboard. Simi- larly, 224-254 are shadow codes of 160-191. Also, in PETASCII, the code value for 255 is the same as code 222. Something else to keep in mind is that while code values 128-159 are control codes like the values 0-31, in many cases they have opposite functions.
For example, while code 18 turns reverse printing on, code 146 (18 + 128), which should perform the same function, actually turns reverse printing off. 32