ISO-1155-1978.pdf

INTERNATIONAL STANDARD INTENATIONAL ORGANIZATION FOR STANOAROIATIONOME)I(YHAHA OPAHMBAUMR no CTAHAPTMAUMH*ORGANISATION INTERNATIONALE DE NRMALISATIN Information processing - Use of longitudinal parity to detect errors in information messages Traitement de linformation - Emploi de la parit longitudinale pour la dhection derreurs darts les messages din formation Second edition - 1978-11-15 UDC 681.3.042.4 Descriptors : data processing, error detecting codes, parity check, block check. Ref. No. IS0 1155-1978 (E) Price based on 1 page Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/25/2007 09:36:56 MDTNo reproduction or networking permitted without license from IHS -,-,- FOREWORD IS0 (the International Organization for Standardization) is a worldwide federation of national standards institutes (IS0 member bodies). The work of developing International Standards is carried out through IS0 technical committees. Every member body interested in a subject for which a technical committee has been set up has the right to be represented on that committee. International organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. Draft International Standards adopted by the technical committees are circulated to the member bodies for approval before their acceptance as International Standards by the IS0 Council. International Standard IS0 1155 was developed by Technical Committee ISOITC 97, Computers and information processing. This second edition was submitted directly to the IS0 Council, in accordance with clause 6.13.1 of the Directives for the technical work of ISO. It cancels and replaces the first edition (i.e. IS0 1155-1973), which had been approved by the member bodies of the following countries : Australia Belgium Brazil Canada Czechoslovakia Denmark Egypt, Arab Rep. of France Germany, F.R. Greece Israel Italy Japan New Zealand Peru Poland Romania Spain Sweden Switzerland Thailand United Kingdom U.S.A. U.S.S.R. No member body had expressed disapproval of the document. Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/25/2007 09:36:56 MDTNo reproduction or networking permitted without license from IHS -,-,- INTERNATIONAL STANDARD IS0 1155-1978 (E) Information processing - Use of longitudinal parity to detect errors in information messages 0 INTRODUCTION In data communication systems the information formats and the redundancy in the data to be transmitted differ widely from one application to another. It is therefore clear that a number of classes of error protection systems may be required. This International Standard defines one method of error detection which satisfies a wide range of applications. It consists of accompanying the data block or text by one checking character (in addition to character parity) and it is often referred to as the “Longitudinal Parity Method”. 1 SCOPE AND FIELD OF APPLICATION This International Standard specifies a method for detecting errors in information messages by attaching one block check character to the transmitted information block (or text) and checking this character when it is received. The method of correcting errors when they are detected is subject to the particular application and is performed at a higher level. The method is applicable to systems which use the 7-bit coded character set which is the subject of IS0 646, 7-bit coded character set for information processing interchange, and the basic mode of implementing this 7-bit code in data communication systems, which is the subject of IS0 1745, Information processing - Basic mode control procedures for data communication systems. The rules for generating the character parity bits, according to IS0 1177, Information processing - Character structure for start/stop and synchronous transmission, are that the character parity sense shall be odd in synchronous systems and even in asynchronous systems. 2 RULES FOR GENERATING THE LONGITUDINAL PARITY BLOCK CHECK CHARACTER 2.1 Block check character 2.1.1 The block check character shall be composed of 7 bits plus a parity bit. 2.1.2 Each of the first 7 bits of the block check character shall be the modulo 2 binary sum of every element in the same bit 1 to bit 7 column of the successive character of the transmitted block. 2.1.3 The longitudinal parity of each column of the block, including the block check character, shall be even. 2.1.4 The sense of the parity bit of the block check character shall be the same as for the information characters (odd for synchronous transmission, even for asynchronous transmission). 2.2 Summation 2.2.1 The summation to obtain the block check character shall be started by the first appearance of either SOH (Start of Heading) or STX (Start of Text). 2.2.2 The starting character shall not be included in the summation. 2.2.3 If an STX character appears after the summation has been started by SOH, then the STX character shall be included in the summation as if it were a text character. 2.3 With the exception of SYN (Synchronous Idle), all the characters which are transmitted after the start of the block check summation shall be included in the summation, including the ETB (End of Transmission/Block) or ETX (End of Text) control character which signals that the next following character is the block check character. 2.4 No character, SYN or otherwise, shall be inserted between the ETB or ETX character and the block check character. 1 Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/25/2007 09:36:56 MDTNo reproduction or networking permitted without license from IHS -,-,-