C0 and C1 control codes
control characters in Unicode, ranging from U+0000 to U+001F and U+007F (C0), and from U+0080 to U+009F (C1)
The C0 and C1 control code or control character sets define control codes for use in text by computer systems that use ASCII and derivatives of ASCII. The codes represent additional information about the text, such as the position of a cursor, an instruction to start a new line, or a message that the text has been received.
C0 codes are the range 00HEX–1FHEX and the default C0 set was originally defined in ISO 646 (ASCII). C1 codes are the range 80HEX–9FHEX and the default C1 set was originally defined in ECMA-48 (harmonized later with ISO 6429). The ISO/IEC 2022 system of specifying control and graphic characters allows other C0 and C1 sets to be available for specialized applications, but they are rarely used.
C0 controls
ASCII defines 32 control characters, plus the DEL character. This large number of codes was desirable at the time, as multi-byte controls would require implementation of a state machine in the terminal, which was very difficult with contemporary electronics and mechanical terminals. Many of the controls were designed for terminals to transmit large messages (such as news articles) from one to another, with no computer involved.
Only a few codes have maintained their use: BEL, ESC, and the format effector (FEn) characters BS, HT, LF, VT, FF, and CR. Others are unused or have acquired different meanings such as NUL being the C string terminator. Some data transfer protocols such as ANPA-1312, Kermit, and XMODEM do make extensive use of SOH, STX, ETX, EOT, ACK, NAK and SYN for purposes approximating their original definitions; and some file formats use the "Information Separators" (ISn) such as the Unix info format and Python's splitlines string method.
The names of some codes were changed in ISO 6429:1992 (or ECMA-48:1991) to be neutral with respect to writing direction.
The public source identifies “C0 and C1 control codes” as control characters in Unicode, ranging from U+0000 to U+001F and U+007F (C0), and from U+0080 to U+009F (C1). This brief keeps that definition visible, then builds a research path around control, codes and characters.
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Named sources, stable identifiers and responsible institutions provide the strongest route from overview to verifiable evidence. The source revision retrieved here is dated Aug 23, 2026. The linked authority identifier is Q718147. The first chronological checks are 2022, 1312, 1992 and 1991.
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This entry incorporates text from “C0 and C1 control codes” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.