1、BRITISH STANDARD BS4505-2: 1990 ISO1177:1985 Digital data transmission Part 2 Character structure for start/stop and synchronous transmissionBS4505-2:1990 This British Standard, having been prepared under the directionof the Information Systems Technology Standards Policy Committee, was publishedund
2、er the authority ofthe Board of BSI and comes intoeffect on 30 June 1990 BSI 03-1999 First published in September 1969 Second edition June1990 The following BSI references relate to the work on this standard: Committee reference IST/6 Draft for comment89/62747DC ISBN 0 580 18208 8 Committees respons
3、ible for this British Standard The preparation of this British Standard was entrusted by the Information Systems Technology Standards Policy Committee (IST/-) to Technical Committee IST/6, upon which the following bodies were represented: Association for Payment Clearing Services British Computer So
4、ciety British Telecommunications plc Business Equipment and Information Technology Association Department of Trade and Industry (Information Technology Standards Unit) Department of Trade and Industry (National Physical Laboratory) Electricity Supply Industry in England and Wales Electronic Engineer
5、ing Association HM Treasury (Central Computer and Telecommunications Agency) Institute of Data Processing Management Inter-Universities Computing Committee Joint Network Team National Computing Centre Ltd. National Health Service OFTEL (Office of Telecommunications) Post Office Telecommunication Eng
6、ineering and Manufacturing Association Telecommunications Managers Association Amendments issued since publication Amd. No. Date CommentsBS4505-2:1990 BSI 03-1999 i Contents Page Committees responsible Inside front cover National foreword ii 1 Scope and field of application 1 2 References 1 3 Bit se
7、quencing Start/stop and synchronous operation 1 4 Parity bit Start/stop and synchronous operation 1 5 Parity sense Start/stop and synchronous operation 1 6 DTE reaction to parity error 1 7 Character framing 2 Publications referred to Inside back coverBS4505-2:1990 ii BSI 03-1999 National foreword Th
8、is Part of BS4505 has been prepared under the direction of the Information Systems Technology Standards Policy Committee. It is identical with ISO1177:1985, “Information processingCharacter structure for start/stop and synchronous character oriented transmission”, published by the International Orga
9、nization for Standardization (ISO). It is a revision of BS4505-2:1969 to align the text with ISO1177 which was published subsequently. It supersedes BS4505-2:1969, which is withdrawn. The UK has actively participated, through BSI Technical Committee IST/6, in the development of the international sta
10、ndard. Up-to-date information on existing and projected British Standards publications for Open Systems Interconnection is included in the Basic List, published as part of the BSI Information Technology Service (BITS) initiative. For details contact: Marketing Department, BSI, Linford Wood, Milton K
11、eynes, MK146LE The Technical Committee has reviewed the provisions of ISO646 and ISO2047, to which reference is made in the text, and has decided that they are acceptable for use in conjunction with this standard. Copies may be obtained from: Sales Department, BSI, Linford Wood, Milton Keynes, MK146
12、LE A British Standard does not purport to include all the necessary provisions of a contact. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Cross-references International standard
13、 Corresponding British Standard ISO2022:1986 BS6856:1987 Specification for code extension techniques for United Kingdom7-bit and8-bit coded character sets (Identical) ISO4873:1986 BS6006:1987 Specification for structure and rules for implementation of United Kingdom8-bit coded character set (Identic
14、al) Summary of pages This document comprises a front cover, an inside front cover, pagesi andii, pages1 and2, an inside back cover and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on theinsid
15、e front cover.ISO1177:1985(E) BSI 03-1999 1 1 Scope and field of application This International Standard specifies the character structure to be used for serial-by-bit start/stop and synchronous data transmission systems using the7-bit coded character set which is the subject of ISO646 1) , the8-bit
16、 coded character set which is the subject of ISO4873 and extensions to these coded character sets which are the subject of ISO2022. It also specifies the parity sense to be used with the7-bit coded character set. It applies to the information transfer through the interface standardized by CCITT and
17、IEC/ISO between the data terminal equipment, DTE, and data circuit-terminating equipment, DCE, as defined in the relevant CCITT V and X series Recommendations. 2 References ISO646, Information processing ISO 7-bit coded character set for information interchange. ISO2022 , Information processing ISO
18、7-bit and8-bit coded character sets Code extension techniques 2) . ISO2047, Information processing Graphical representations for the control characters of the 7-bit coded character set. ISO4873, Information processing 8-bit code for information interchange Structure and rules for implementation 3) .
19、 3 Bit sequencing Start/stop and synchronous operation In serial working data transmission systems, the chronological order of transmission of the information bits shall correspond to either a) the bit identification b 1to b 7as defined in the7-bit code table of ISO646 with the least significant bit
20、 transmitted first; or b) the bit identification b 1to b 8as defined in the8-bit code table of ISO4873 with the least significant bit transmitted first. When the rank in the combination represents the order of the bit in binary numbering, the bits shall be transmitted in serial, working with the low
21、 order bit first. The numerical meaning corresponding to each information bit considered in isolation is that of the digit in accordance with the definitions of these conditions for two-condition transmission systems. 4) 4 Parity bit Start/stop and synchronous operation For7-bit working, a parity bi
22、t shall be added to every character and shall be located in the eighth position, b 8 , and is therefore transmitted after the seven significant bits for the character. 5 Parity sense Start/stop and synchronous operation For start/stop systems using7-bit working, the parity bit shall be chosen in suc
23、h a way that the number of “ONE” bits is even in the sequence of eight bits thus formed. For synchronous systems using7-bit working, the parity bit shall be chosen in such a way that the number of “ONE” bits is odd in the sequence of eight bits thus formed. 6 DTE reaction to parity error The detecti
24、on of a character out-of-parity in7-bit working may be represented by a) a reverse question mark graphic character or a representation of the capital letter SB(seeISO2047) provided that this letter occupies a single character position on screen or printer, and could have been entered by a single key
25、 stroke whilst recognizing that it may be difficult to achieve a legible “SB” character for some matrix printers or displays where the characters are printed or visually displayed; and/or b) recording of the1/10 (SUB) character in the tape or other storage medium, where provided. 1) This character s
26、et is also standardized by CCITT: International Alphabet No.5, Recommendation V3. 2) At present at the stage of draft. (Revision of ISO2022-1982.) 3) At present at the stage of draft. 0 for a unit corresponding to condition A (Travail = Space), and 1 for a unit corresponding to condition Z (Repos =
27、Mark), 4) Condition A is that which corresponds to the start signal of a standardized start/stop apparatus, and condition Z is that which corresponds to a stop signal. For further details see the CCITT list of definitions of essential telecommunication terms.ISO1177:1985(E) 2 BSI 03-1999 Where a SUB
28、 character occurs in a received transmission, or is presented to a DTE via a storage medium, for example paper tape, then the reaction should be as in a) and b) above. 7 Character framing 7.1 Start/Stop operation In start/stop systems using the7-bit or8-bit coded character sets, ten or eleven unit e
29、lements shall be used per character. The first information bit of the transmitted coded combinations shall be preceded by a start element corresponding to condition A (Travail = Space). The duration of this start element shall be one unit interval at the data signalling rate at the transmitting inte
30、rface. The combination of seven information elements completed by its parity element or of eight information elements shall be followed by a stop element corresponding to condition Z (Repos=Mark). As for the stop element duration the following provisions should be observed depending on the types of
31、network used: a) For systems using the7-bit or8-bit coded character sets over the general switched telephone and telegraph networks with electromechanical data terminal equipment operating at data signalling rates up to and including200bps, the stop element duration at the transmitter shall be TWO u
32、nit intervals at the data signalling rate of the transmitter. In other cases the use of a stop element with a duration of ONE unit interval is recommended. However, this is subject to mutual agreement between the parties concerned. Similar situations when a ONE unit interval stop element can be used
33、 may apply to leased circuits. The start/stop receivers should be capable of correctly receiving start/stop signals comprising a single-unit stop element, whose duration will be reduced by a time interval equal to the deviation corresponding to the degree of gross start/stop distortion permitted at
34、the receiver input. However, for electromechanical equipment which is required to use a two-unit stop element(11-unit alphabet) with a data signalling rate of200bps or less, receivers should be capable of correctly receiving signals with a stop element reduced to one unit. b) For public asynchronous
35、 data networks, data terminal equipment using the7-bit coded character set should use a stop element lasting at least two unit intervals. However, the receivers may only be capable of correctly receiving signals when the stop element is not reduced below one unit interval (even in the presence of di
36、stortion). The time between the end of the stop element of a character and the beginning of the start element of the next character may be of any duration; the polarity of the signal during this time shall be the same as that of the stop element. 7.2 Synchronous operation In synchronous systems eigh
37、t bits per character shall be used. For7-bit working, these eight bits comprise the seven information bits followed by the parity bit. The time between the end of the last bit of a character and the beginning of the first bit of the next character shall be zero time or a multiple of the unit interva
38、l at the data signalling rate of the transmitter. When character synchronism is required to be maintained, this time interval shall be zero or a multiple of the character interval. In systems that use the eighth bit for parity, the parity sense shall be maintained.BS4505-2:1990 BSI 03-1999 Publicati
39、ons referred to See national forewordBSI 389 Chiswick High Road London W4 4AL | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
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