1、CCITT RECflNrT.50 92 48b259L 057bLb 426 INTERNATIONAL TELECOMMUN CATION UN ION CCITT THE INTERNATIONAL TELEGRAPH AND TELEPHONE CONSULTATIVE COMMITTEE TERMINAL EQUIPMENT AND PROTOCOLS FOR TELEMATIC SERVICES T.50 (09/92) INTERNATIONAL REFERENCE ALPHABET (IRA) (FORMERLY INTERNATIONAL ALPHABET No. 5 or
2、IA5) INFORMATION TECHNOLOGY - 7-BIT CODED CHARACTER SET FOR INFORMATION INTERCHANGE i Recommendation T.50 COPYRIGHT International Telecommunications Union/ITU TelecommunicationsLicensed by Information Handling ServicesFOREWORD The CCITT (the International Telegraph and Telephone Consultative Committ
3、ee) is a permanent organ of the International Telecommunication Union (ITU). CCITT is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis. The Plenary Assembly of CCIIT which meets
4、 every four years, establishes the topics for study and approves Recommendations prepared by its Study Groups. The approval of Recommendations by the members of CCITT between Plenary Assemblies is covered by the procedure laid down in CCIIT Resolution No. 2 (Melbourne, 1988). Recommendation (revised
5、) T.50 was prepared by Study Group VI11 and was approved under the Resolu- tion No. 2 procedure on the 18th of September 1992. CCIT NOTES 1) telecommunication administration and a recognized private operating agency. 2) In this Recommendation, the expression “Administration” is used for conciseness
6、to indicate both a A list of abbreviations used in this Recommendation can be found in Annex C. O ITU 1993 All rights reserved. No part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in
7、 writing from the ITU. COPYRIGHT International Telecommunications Union/ITU TelecommunicationsLicensed by Information Handling ServicesCCITT RECflN*T*50 92 48b259L 057bl128 2T9 Recommendation T.50 INTERNATIONAL REFERENCE ALPHABET (IRA) (Formerly International Alphabet No. 5 or IA5) Information techn
8、ology - 7-bit coded character set for information interchange (revised 1992) 1 Scope 1.1 This Recommendation specifies a set of 128 characters, (control characters and graphic characters such as letters, digits and symbols) with their coded representation. Most of these characters are mandatory and
9、unchangeable, but provision is made for some flexibility to accommodate national and other requirements. 1.2 This Recommendation specifies a 7-bit coded character set with a number of options. It also provides guidance on how to exercise the options to define specific national versions and applicati
10、on-oriented versions. Furthermore, it specifies the International Reference Version (IRV) in which such options have been exercised. 1.3 This character set is primarily intended for the interchange of information among data processing systems and associated equipment, and within data communication s
11、ystems. The need for graphic characters and control functions in data processing has also been taken into account in determining this character set. 1.4 This character set is applicable to alphabets of the Latin script. 1.5 insufficient for particular applications. Procedures for the use of these co
12、ntrol characters are specified in IS0 2022. This character set allows the use of control characters for code extension where its character set is 1.6 The definitions of the control characters mentioned in this Recommendation are specified in Annex A. It is assumed that data associated with them are
13、to be processed serially in a forward direction. when they are included in strings of data which are processed other than serially in a forward direction, or when they are included in data formatted for fixed-record processing, they may have undesirable effects or may require additional special trea
14、tment to ensure that they result in their desired function. 1.7 (1991). This is a paired Recommendation/International Standard, equivalent in technical content to ISO/IEC 646 2 Conformance and implementation 2.1 Conformance 2.1.1 Conformance of information interchange A coded-character-data-element
15、(CC-data-element) within coded information for interchange is in conformance with this Recommendation if all the coded representations of characters within that CC-data-element conform to the requirements of 0 8.1. A claim of conformance shall identify the version adopted in accordance with $0 8.2 t
16、o 8.4. Recommendation T.50 (09/92) 1 COPYRIGHT International Telecommunications Union/ITU TelecommunicationsLicensed by Information Handling ServicesCCITT RECMN*T*SO 92 48b2591 057b129 135 I 2.1.2 Conformance of devices A device is in conformance with this Recommendation if it conforms to the requir
17、ements of $2.1.2.1, and either or both of ss2.1.2.2 and 2.1.2.3 below. A claim of conformance shall identify the version adopted. 2.1.2.1 Device description A device that conforms to this Recommendation shall be the subject of a description that identifies the means by which the user may supply char
18、acters to the device, or may recognize them when they are made available to the user, as specified respectively in $0 2.1.2.2 and 2.1.2.3 below. 2.1.2.2 Originating devices An originating device shall allow its user to supply any sequence of characters from the version adopted, and shall be capable
19、of transmitting their coded representations within a CC-data-element. 2.1.2.3 Receiving devices A receiving device shall be capable of receiving and interpreting any coded representations of characters that are within a CC-data-element, and that conform to $ 2.1.1, and shall make the corresponding c
20、haracters available to its user in such a way that the user can identify them from among those of the version adopted, and can distinguish them from each other. 2.2 Implementation The use of this character set requires definitions of its implementation in various media. For example, these could incl
21、ude punched tapes, punched cards, magnetic and optical interchangeable media and transmission channels, thus permitting interchange of data to take place either indirectly by means of an intermediate recording on a physical medium, or by local connection of various units (such as input and output de
22、vices and computers) or by means of data transmission equipment. The implementation of this coded character set in physical media and for transmission, taking into account the need for error checking, is the subject of other Recommendations. 3 Normative references The following standards contain pro
23、visions which, through reference in this text, constitute provisions of this Recommendation. At the time of publication, the editions indicated were valid. All standards are subject to revision, and parties to agreements based on this Recommendation are encouraged to investigate the possibility of a
24、pplying the most recent editions of the standards listed below, IS0 2022: 1986 Information processing - IS0 7-bit and code A set of unambiguous rules that establishes a character set and the one-to-one relationship between the characters of the set and their representation by one or more bit combina
25、tions. 4.6 coded character-data-element (CC-data-element) An element of interchanged information that is specified to consist of a sequence of coded representations of characters, in accordance with one or more identified standards for coded character sets. Note 1 - In a communication environment ac
26、cording to the Reference Model for Open Systems Interconnection of Recommendation X.200 (IS0 7498) a CC-data-element will form all or part of the information that corresponds to the application user data and the presentation protocol data unit (PPDU) defined in that Recommendation. Note 2 - When inf
27、ormation interchange is accomplished by means of interchangeable media, a CC-data- element will form all or part of the information that corresponds to the user data, and not that recorded during formatting and initialization. 4.7 code extension The techniques for the encoding of characters that are
28、 not included in the character set of a given code. 4.8 code table A table showing the character allocated to each bit combination in a code. 4.9 control character A control function the coded representation of which consists of a single bit combination. 4.10 control function An action that affects
29、the recording, processing, transmission or interpretation of data and that has a coded representation consisting of one or more combinations. 4.11 device A component of infomation processing equipment which can transmit, and/or can receive, coded information within CC-data-elements. Note - It may be
30、 an input/output device in the conventional sense, or a process such as an application program or gateway function. 4.12 graphic character A character, other than a control function, that has a visual representation normally handwritten, printed or displayed, and that has a coded representation cons
31、isting of one or more bit combinations. 4.13 graphic symbol A visual representation of a graphic character or of a control function. Recommendation T.50 (09/92) 3 COPYRIGHT International Telecommunications Union/ITU TelecommunicationsLicensed by Information Handling ServicesCCITT RECMNST-SO 92 48b25
32、9L 057bL3L 893 Bit bl b6 bs b4 b3 Weight 64 32 16 8 4 4.14 position b2 bl 2 1 That part of a code table identified by its column and row co-ordinates. 4.15 repertoire A specified set of characters that are represented by means of one or more bit combinations of a coded character set. 4.16 user A per
33、son or other entity that invokes the services provided by a device. Note I - This entity may be a process such as an application program if the “device” is a code convertor or a gateway function, for example. Note 2 - The characten, as supplied by the user or made available to the user, may be in th
34、e form of codes local to the device, or of non-conventional visible representations, provided that P 2.1.2 above is satisfied. 5 Notation, code table and names 5.1 Notation The bits of the bit combinations of the 7-bit code are identified by b7, b6, b5, b4, b3, bp, and bi, where b7 is the highest-or
35、der, or most-significant, bit and b1 is the lowest order, or least-significant, bit. “he bit combination may be interpreted to represent integers in the range O to 127 in binary notation by attributing the following weights to the individual bits: In this Recommendation, the bit combinations are ide
36、ntified by notations of the form xly, where x is a number in the range O to 7 and y is a number in the range O to 15. The correspondence between the notations of the form dy and the bit combinations consisting of the bits b7 to b1 is as follows: - x is the number represented by b7, b6, and b5, where
37、 these bits are given the weights 4, 2 and 1 respectively; - y is the number represented by b4, b3, b, and b1, where these bits are given the weights 8, 4, 2 and I respectively. The notations of the form xly are the same as those used to identify code table positions, where n is the column number an
38、d y the row number (see 8 9). 4 Recommendation T.50 (09/92) COPYRIGHT International Telecommunications Union/ITU TelecommunicationsLicensed by Information Handling ServicesCCITT RECMN*T=5 i2 m LiBb259L 057bL32 72T H 5.2 Code table A 7-bit code table consists of 128 positions arranged in 8 columns an
39、d 16 rows. The columns are numbered O to 7 and the rows O to 15. The code table positions are identified by notations of the form dy, where x is the column number and y is the row number. The position of the code table is in one-to-one correspondence with the bit combinations of the code. The notati
40、on of a code table position, of the form xly, is the same as that of the corresponding bit combination. The allocation of individual characters to the bit combinations of the 7-bit code is specified in $8 6.2 to 6.5. 5.3 Names This Recommendation assigns one name to each character. In addition, it s
41、pecifies an acronym for each control character and for the character SPACE, and a graphic symbol for each graphic character. By convention, only capital letters, space and hyphen are used for writing the names of the characters. For acronyms only capital letters and digits are used. It is intended t
42、hat the acronyms and this convention be retained in all translation of the text. The names chosen to denote graphic characters are intended to reflect their customary meaning. However, this Recommendation does not define and does not restrict the meanings of graphic characters. Neither does it speci
43、fj a particular style or font design for the graphic characters when imaged. 6 Specification of the coded character set 6.1 Structure The coded character set of this Recommendation shall have the following structure: - a CO control character set of up to 32 control characters allocated to positions
44、010 to 1/15: - the graphic character SPACE (SP) allocated to position YO; - a GO graphic character set of up to 94 graphic characters allocated to positions 2/1 to 7/14; - the character DELETE (DEL) allocated to position 7/15. 6.2 Control characters The control Characters allocated to positions O/O
45、to 1/15 shall be as specified in Annex A. 6.3 Character SPACE The acronym of the character SPACE is SP and its coded representation is WO. This character is a graphic character; it has a visual representation consisting of the absence of a graphic symbol. Recommendation T.50 (09/92) 5 COPYRIGHT Inte
46、rnational Telecommunications Union/ITU TelecommunicationsLicensed by Information Handling ServicesCCITT RECMN*T.50 92 W 4Bb259L 057bL33 bbb W CO GO TOB1 1580-93 FIGURE ln.50 Structure of the 7-bit coded Character set 6.4 Graphic characters The 94-bit combinations 2/l to 7/14 are used for the represe
47、ntation of graphic characters as specified in $8 6.4.1,6.4.2 and 6.4.3. Ail graphic Characters shall be spacing characters, that is, they cause the active position to advance by one character position. 6.4.1 Unique graphic character allocations A unique graphic character is allocated to each of the
48、82-bit combinations 2/1, Z2, 2/5 to 3/15, 4/1 to 5/10, 5/15 and 6/1 to 7/10. These characters are specified in Table lT.50. 6.4.2 Alternative graphic character allocations Two alternative graphic characters are allocated to each of the bit combinations 20 and 2/4. These characters are specified in T
49、able 2T.50. 6 Recommendation T.50 (09/92) COPYRIGHT International Telecommunications Union/ITU TelecommunicationsLicensed by Information Handling ServicesCCITT RECMN*T.50 92 4862593 0576334 5T2 Graphic symbol ! 8 to specify the GO ser - to ailocate to each of the bit combinations 2/3 and U4 one of the alternative graphic characters specified in $ 6.4.2; to allocate to each of the bit combinations 4/0, 5/11 to 5/14,6/0 and 7/11 to 7/14 a unique graphic character, or to declare the bit combination unused. - A graphic character allocated to a bit combination specified in Q$ 6.4.1 and 6.4
