AS 1953-1987

Specifies methods of extending the 7-bit code, remaining in a 7-bit environment or increasing to an 8-bit environment. These techniques are described in interrelated clauses dealing with the extension of the 7-bit code remaining in a 7-bit environment, the structure of a family of 8-bit codes, the extension of an 8-bit code remaining in an 8-bit environment and the relationship between the 7-bit code and an 8-bit code. This Standard also describes the structure of families of codes which are related to the code of AS 1776 by their structure. This Standard is technically identical with ISO 2022:1986.

This International Standard specifies methods of extending the 7-bit code, remaining in a 7-bit environment or increasing to an 8-bit environment. These techniques are described in four interrelated clauses dealing respectively with- the extension of the 7-bit code remaining in a 7-bit environment;- the structure of a family of 8-bit codes;- the extension of an 8-bit code remaining in an 8-bit environment;- the relationship between the 7-bit code and an 8-bit code.This International Standard also describes the structure of families of codes which are related to the code of ISO 646 by their structure. Code extension techniques are classified and some classes are given a structure in this International Standard. Specific assignments of bit combinations to relate individual character sets and control functions with their invocation or designation are to be made in accordance with ISO 2375 (see annex A).While the 7-bit code of ISO 646 is the agreed code for information interchange, an 8-bit code as described in this International Standard is provided for information interchange within an 8-bit environment.The 7-bit code of ISO 646 allows the representation of up to 128 characters. Additionally, ISO 646 allows the representation of other graphic characters by the combination of two or more graphic characters with the control characters BACKSPACE or CARRIAGE RETURN. In some instances, the character set of ISO 646 lacks sufficient control functions or graphic characters to satisfy the needs of an application. These needs may be satisfied by means of code extension which is the subject of this International Standard.The principles established in this International Standard may be utilized to form supplementary code extension facilities. For example ISO 6429 has followed such a procedure to formulate some parameterized control functions. This International Standard presents a review of the salient structure of the 7-bit code and then builds upon that structure to specify various means of extending the control function and graphic sets of the code. It alsospecifies structures and techniques to construct and formalize codes related to the 7-bit code. These related codes are structured so as to allow application-depend ent usa ge w ithou t pre venting the interchangeability of data employing them. It describesa) the structure of the 7-bit code;b) the extension of the 7-bit code, remaining in a 7-bit environment and making use of code extension techniques;c) the structure of a family of 8-bit codes, remaining compatible with the 7-bit structure;d) the extension of an 8-bit code, remaining in a 8-bit environment, and making use of code extension techniques.In order to use identical techniques in each of the above cases, and to facilitate conversion between them, standard rules for code extension are necessary. This has the advantage ofa) reducing the risk of conflict between systems required to inter-operate;b) permitting provision for code extension in the design of systems;c) providing standardized methods of calling into use agreed sets of characters;d) allowing the interchange of data between 7-bit and 8-bit environments, etc.Code extension techniques are designed to be used for data to be processed serially in a forward direction. Use of these techniques in strings of data which are processed other than serially in a forward direction or included in data formatted for fixed-length record processing may have undesirable results or may require additional special treatment to ensure correct interpretation.