ASA control characters are simple printing command characters used by mainframe printers to control the movement of paper through line printers. These commands are presented as special characters in the first column of each text line to be printed, and affect how the paper is advanced before the line is printed.
"ASA" is the abbreviation of the American Standards Association, a former name for the American National Standards Institute (ANSI), which is believed to have sanctioned these control characters.
Overstriking can be used to make boldface text by printing the same line twice without advancing the paper. It can also be used to make underlined text by printing a line of underscore characters atop the text.
Mainframe printers have 12 channels (1 through 9 and A through C) that can be assigned a fixed position on the page, allowing the printer to skip a variable distance down the page to a fixed location. Normally only channel 1 is preassigned, to the top of the page.
ASA carriage control characters are still used for printer output from mainframe applications and software today, and are not limited to seasoned software or applications dating from the days of the line printer. ASA carriage control characters are interpreted by other software before being printed on modern computer printers.
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In computing and telecommunication, a control character or non-printing character is a code point (a number) in a character set, that does not in itself represent a written symbol. It is in-band signaling in the context of character encoding. All entries in the ASCII table below code 32 (technically the C0 control code set) and 127 are of this kind, including BEL (which is intended to cause an audible signal in the receiving terminal), SYN (which is a synchronization signal), and ENQ (a signal that is intended to trigger a response at the receiving end, to see if it is still present). The Extended Binary Coded Decimal Interchange Code (EBCDIC) character set contains 65 control codes, including all of the ASCII control codes as well as additional codes which are mostly used to control IBM peripherals. Unicode makes a distinction between Control characters (C0 and C1 control codes) versus Formatting characters (such as the Zero-width non-joiner).
Other characters are printing, printable, or graphic characters, except perhaps for the "space" character (see ASCII printable characters).
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