ASCII format for network interchange
also
- std-80
Extracted elements (15)
Deviations from the ASCII standard 'may create serious difficulties in information interchange and should be used only with full cognizance of the parties involved,' establishing interoperability as the primary motivation for the standard.
No specific semantic meaning is prescribed for graphic characters beyond what users understand, and no type style is specified for printing or display; applications may stylize individual graphics (e.g., 2/1 as logical OR, 5/15 as logical NOT) for their own purposes.
The relative collation sequence of any two characters is defined solely by their binary values (b7 through b1), providing a deterministic and implementation-neutral sort order without requiring a separate collation table.
The standard deliberately does not define how the coded set is recorded on any physical medium, nor does it include redundancy, error control, data communication character structure, code extension techniques, or graphic representation of control characters. These concerns are left to other specifications.
Break (end-of-line) characters are defined by the receiving remote host, not by a global standard; SRI uses period (ASCII 2/14) while UCLA uses carriage return (0/13). Implementations must negotiate or be configured for the remote host's convention.
LF (Line Feed) may optionally carry the meaning 'New Line' (movement to first position on next line) rather than simply advancing the printing line, but use of this convention requires explicit agreement between sender and recipient.
The characters @, [, \, ], ^, `, {, |, }, ~, # (positions 4/0, 5/11–5/15, 6/0, 7/11–7/14, 2/3) should not be used in international interchange without prior agreement between sender and recipient, due to differing national assignments.
The code may be identified by the notation 'ASCII' or 'USASCII'; to designate a specific edition, the last two digits of the year of issue may be appended (e.g., 'ASCII 63'). Without a year suffix, the notation refers to the latest issue.
7-bit ASCII embedded in an 8-bit byte (high-order bit zero) is to be used over HOST-HOST primary connections on the ARPANET.
Communication Control characters include SOH (start of heading/routing), STX (start of text entity, terminates heading), ETX (end of text), EOT (end of transmission), ENQ (enquiry/WRU), ACK (affirmative acknowledge), NAK (negative acknowledge), SYN (synchronous idle), DLE (data link escape), and ETB (end of transmission block).
DEL (7/15, all-ones bit pattern) is used to erase or obliterate unwanted characters on perforated tape; it is explicitly noted not to be a control character in the strict sense, distinguishing it from the 32 true control characters in columns 0 and 1.
ESC (Escape, 1/11) is a prefix character that affects the interpretation of a limited number of contiguously following characters, providing a code extension mechanism for supplementary characters beyond the 128-position table.
Four Information Separator characters define a mandatory hierarchy: FS (File Separator) is most inclusive, followed by GS (Group Separator), RS (Record Separator), and US (Unit Separator) as least inclusive. Content and length of the delimited units are not specified by the standard.
The ASCII table defines 33 control characters (columns 0–1), a space character, 94 graphic characters (columns 2–7), and a DEL character, for 128 total code points. Control characters are categorized as Communication Controls (CC), Format Effectors (FE), or Information Separators (IS).
Standard 7-bit ASCII is embedded in an 8-bit byte whose high-order bit is always 0, yielding 128 code positions arranged as 8 columns (b7–b5) by 16 rows (b4–b1). The column number is the decimal value of bits b7b6b5 and the row number is the decimal value of bits b4b3b2b1.