1、INTERNATIONAL STANDARD ISOAEC Third edition 1991-12-15 Information technology - IS0 7-bit coded character set for information interchange Technologies de /information - Jeu IS0 de caract code : A set of unambiguous rules that establishes a character set and the one-to- one relationship between the c
2、haracters of the set and their bit combinations. 1) To he published. 2 4.6 coded-character-data-element (CC-data-element) : An element of interchanged information that is ISO/IEC 646:1991 (E) specified to consist of a sequence of coded representations of characters, in accordance with one or more id
3、entified standards for coded character sets. NOTE 2 - In a communication environment according to the Reference Model for Open Systems Interconnection (IS0 74%). a CC-data-element will form all or part of the information that corresponds to the Presentation - Protocol -Data - Unit (PPDU) defined in
4、that International Standard. NOTE 3 - When information 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 tec
5、hniques for the encoding of characters that are 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 combina
6、tion. 4.10 control function : An action that affects the recording, processing, transmission, or interpretation of data, and that has a coded representation consisting of one or more bit combinations. 4.11 device : A component of information processing equipment which can transmit, and/or receive, c
7、oded information within CC-data-elements. NOTE 4 - It may be an input/output device in the conventional sense, or a process such as an application program or gateway function. 4.12 escape sequence : A string of bit combinations that is used for control purposes in code extension procedures. The firs
8、t of these bit combinations represents the control function ESCAPE. 4.13 Final Byte : The bit combination that terminates an escape sequence or a control sequence. 4.14 graphic character : A character, other than a control function, that has a visual representation normally handwritten, printed or d
9、isplayed, and that has a coded representation consisting of one or more bit combinations. 4.15 graphic symbol : A visual representation of a graphic character or of a control function. 4.16 repertoire : A specified set of characters that are represented by means of one or more bit combinations of a
10、coded character set. 4.17 user : A person or other entity that invokes the services provided by a device. NOTE 5 - 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 h - The characters, as supplied by the user or m
11、ade available to him, may be in the device, or of non-conventional visible representations, provided that 2.1.2 above is satisfied. 5 Notation, code table and names 5.1 Notation form of codes local to the The bits of the bit combinations of the 7-bit code are identified by b. bb, bg. b4, b3, b and b
12、l, where is the highest-order, or most-significant, bit and bl is the lowest-order, or least-significant, bit. The bit combinations may be interpreted to represent integers in the range 0 to 127 in binary notation by attributing the following weights to the individual bits: ISO/IEC 646:1991 (E) Bit
13、: b7 b6 b5 b4 b3 b2 bl Weight : 64 32 16 8 4 2 1 In this International Standard, the bit combinations are identified by notations of the form x/y, where x is a number in the range 0 to 7 and y is a number in the range 0 to 15. The correspondence between the notations of the form x/y and the bit comb
14、inations consisting of the bits b7 to bt is as follows: - x is the number represented by b7, bh and b5 where these bits are given the weights 4, 2 and 1 respectively; - y is the number represented by b4. b3, b2 and br where these bits are given the weights 8, 4, 2 and 1 respectively. The notations o
15、f the form x/y are the same as those used to identify code table positions, where x is the column number and y the row number (see 5.2). 5.2 Code table A 7-bit code table consists of 128 positions arranged in 8 columns and 16 rows. The columns are numbered 0 to 7 and the rows 0 to 15. The code table
16、 positions are identified by notations of the form x/y, where x is the column number and y is the row number. The positions of the code table are in one-to-one correspondence with the bit combinations of the code. The notation of a code table position, of the form x/y, is the same as that of the cor
17、responding bit combination. 5.3 Names This International Standard assigns one name to each character. In addition, it specifies an acronym for each control character and for the characters SPACE and DELETE, and a graphic symbol for each graphic character. By convention, only capital letters, space a
18、nd hyphen are used for writing the names of the characters. For acronyms only capital letters and digits are used. It is intended that the acronyms and this convention be retained in all translations of the text. The names chosen to denote graphic characters are intended to reflect their customary m
19、eaning. However, this International Standard does not define and does not restrict the meanings of graphic characters. Neither does it specify 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
20、 this International Standard shall have the following structure. - a CO control character set of up to 32 control characters; - the graphic character SPACE (SP); - a GO graphic character set of up to 94 graphic characters; - the character DELETE (DEL). ISO/IEC 646:1991 (E) GO Ii= DEI Figure 1 - Stru
21、cture of the 7-bit coded character set 6.2 Control characters The control characters of the CO set shall be represented by bit combinations as specified in annex A. 6.3 Character SPACE The acronym of the character SPACE is SP and it is represented by bit combination 2/O. This character is a graphic
22、character, it has a visual representation consisting of the absence of a graphic symbol. 6.4 Graphic characters The 94 bit combinations 2/l to 7/14 are used for the representation of graphic characters as specified in 6.4.1, 64.2 and 6.4.3. All graphic characters shall be spacing characters, that is
23、, 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 82 bit combinations 2/l, 2/2, 2/5 to 3/15, 4/l to YlO, 5/15 and 6/l to 7/10. These graphic characters are specified in table 1. 5 I
24、SO/IEC 646:1991 (E) Table 1 - Unique graphic character allocations Graphic Name CO QUOTATION MARK m PERCENT SIGN 2/5 84 AMPERSAND 2/6 ; APOSTROPHE 217 LEFT PARENTHESIS 218 RIGHT PARENTHESIS 2/g * ASTERISK 2/10 + PLUS SIGN 2/11 9 COMMA 2/12 HYPHEN-MINUS 2/13 i FULL STOP 2/14 SOLIDUS 2/15 0 DIGIT ZERO
25、 3/O : DIGIT ONE 3/l DIGIT TWO 312 3 DIGIT THREE 3/3 4 DIGIT FOUR 314 z DIGIT FIVE 3/5 DIGIT SIX 316 i DIGIT SEVEN 3/7 DIGIT EIGHT 3/8 9 DIGIT NINE 3/g . . COLON 3/10 . , SEMICOLON 3/11 GREATER-THAN SIGN 3/14 ? QUESTION MARK 3115 A LATIN CAPITAL LETTER A 4/l F LATIN CAPITAL LETTER B 412 LATIN CAPITA
26、L LETTER C 4/3 D LATIN CAPITAL LETTER D 414 E LATIN CAPITAL LETTER E 4/5 F LATIN CAPITAL LETTER F 4/S G LATIN CAPITAL LETTER G 417 H LATIN CAPITAL LETTER H 4/G I LATIN CAPITAL LETTER I 4/g 3 LATIN CAPITAL LETTER J 4/10 K LATIN CAPITAL LETTER K 4/11 L LATIN CAPITAL LETTER L 4/12 M LATIN CAPITAL LETTE
27、R M 4/13 i LATIN CAPITAL LETTER N 4114 LATIN CAPITAL LETTER 0 4115 P LATIN CAPITAL LETTER P 5/O LATIN CAPITAL LETTER Q 5/l LATIN CAPITAL LETTER R 512 S LATIN CAPITAL LETTER S 5/3 (continued) ISO/IEC 646:1991 (E) Table 1 - Unique graphic character allocations Graphic Symbol Name Coded representation
28、T LATIN CAPITAL LETTER T 514 U LATIN CAPITAL LETTER U 5/5 V LATIN CAPITAL LETTER V 5/6 W LATIN CAPITAL LETTER W 517 X LATIN CAPITAL LETTER X 518 Y LATIN CAPITAL LETTER Y 519 Z LATIN CAPITAL LETTER Z 5/10 LOW LINE 5115 a LATIN SMALL LETTER A 6/l b LATIN SMALL LETTER B 612 : LATIN SMALL LETTER C 613 L
29、ATIN SMALL LETTER D 614 e LATIN SMALL LETTER E 6/5 f LATIN SMALL LETTER F W6 9 LATIN SMALL LETTER G 617 h LATIN SMALL LETTER H w3 i LATIN SMALL LETTER I 6/g J LATIN SMALL LETTER J 6/10 k LATIN SMALL LETTER K 6/11 1 LATIN SMALL LETTER L 6112 m LATIN SMALL LETTER M 6/13 n LATIN SMALL LETTER N 6114 0 L
30、ATIN SMALL LETTER 0 6115 P LATIN SMALL LETTER P 7/O q LATIN SMALL LETTER Q 7/l r LATIN SMALL LETTER R 712 t LATIN SMALL LETTER S 713 LATIN SMALL LETTER T 7/4 u LATIN SMALL LETTER U 715 V LATIN SMALL LETTER V 7/6 W LATIN SMALL LETTER W 717 X LATIN SMALL LETTER X 7/B Y LATIN SMALL LETTER Y 7/g z LATIN
31、 SMALL LETTER Z 7/10 6.4.2 Alternative graphic character allocations Two alternative graphic characters are allocated to each of the bit combinations 213 and 214. These characters are specified in table 2. Table 2 - Alternative graphic character allocations Graphic Name COdlXl Symbol representation
32、# NUMBER SIGN 213 E POUND SIGN 213 DOLLAR SIGN 214 CURRENCY SIGN 214 7 ISO/IEC 646:1991 (E) Either the character NUMBER SIGN or the character POUND SIGN shall be allocated to bit combination 2/3 and either the character DOLLAR SIGN or the character CURRENCY SIGN shall be allocated to bit combination
33、 2/4 (see clause 8). Unless otherwise agreed between sender and recipient, the graphic symbols f, $ and / I 3 . 1 c 6 - bl 0 0 1 I 02 13 04 15 06 17 08 19 0 IO 1 11 0 12 1 13 0 14 1 15 00 00 00 00 0 1 0 1 0 1 mm 0 1 II IO II 10 II 10 II IO II 1 1 1 1 1 1 1 1 P q b r d e h i j k 0 2 - a - - DEL m - n
34、 - 0 CO Set 11 ISO/IEC 646:1991 (E) Table 5 - Version with the GO set of the IRV I :,.:. :. . oo jjiSiitilii5iii .:;:;:;:#:;:;:;:;: . . . . . . . . . . . . . . . . . . . ._. :;:_.; ,._._.:. :.:.:.:.:.:.:.:.:. .:i_:, 1 :.:.:. :. o 2 : .C._ liii:?:j: . . . . . . . . . . . . . . . . . II _.;,. . . . .
35、. . . . ,.:_._.,. _._._ . . . . . ._., j: :.:.:. alll” :. .:.:.:i.:.:.:.:.:.:.: i.:l:l:.i.:ii ( 8 H 1 1 1 ZE 0 1 1 1 0 51617 P P ?T Q a q Rlblr slcls U e u TF v f v Xlhlx 12 ISO/IEC 646:1991 (E) Annex A (normative) Specification of the CO set A.1 CO set of a version of ISO/IEC 646 Table A.1 - CO set
36、 of ISO/IEC 6429 The CO set of a version of ISO/IEC 646 shall be a sub-set of the CO set of ISO/IEC 6429. The selected control functions shall be used according to their definitions in ISO/lEC 6429. Bit combinations corresponding to control functions not selected shall be declared unused. A.2 CO set
37、 of the IRV If the CO set of the International Reference Version (IRV) is used, it shall be the CO set of ISO/IEC 6429. A.3 Table A.1 Table A.1 shows, for convenience, the CO set of ISOfiEC 6429. For the definition of these control functions see ISO/IEC 6429. 8 13 ISO/IEC 646:1991 (E) Annex B (infor
38、mative) Guidelines for standards derived from ISO/IEC 646 B.l General When drafting national or application-orientated standards based on ISO/IEC 646, it is recommended that the following considerations be taken into account. B.2 Structure of a standard It is recommended that the same structure and
39、editorial style as implemented for ISO/IEC 646 be adopted. All facilities, restrictions and specifications of the standard should be stated clearly in sentences using plain language, rather than being summarized in tables with notes. B.2.1 Control functions The standard should contain the selection
40、of control characters from the CO set of ISO/IEC 6429 and an explicit description of the corresponding control functions. Even where the descriptions are identical with those of ISO/IEC 6429, they should be stated explicitly, and not merely by reference to ISO/IEC 6429. For application-oriented stan
41、dards the specific meaning of the Information Separators and of the Device Controls should be defined. B.2.2 Graphic characters (see 8.3.3) Where there is no need for particular characters, the graphic characters of the International Reference Version (IRV) should be allocated to the same bit combin
42、ations and with the same names as in ISO/IEC 646. B-2.3 Composite graphic characters and repertoire ISO/IEC 646 permits the construction of composite graphic characters by using the control characters BACKSPACE and CARRIAGE RETURN to image two or more graphic characters at the same character positio
43、n. The total number of graphic characters which can be obtained from any version of the character set, with or without using this facility, is called the repertoire. ISO/IEC 646 does not define a particular repertoire. However, as the interpretation and/or the imaging of composite characters may cau
44、se difficulties, agreement between sender and recipient of the data may be required. To minimize the need for such agreements and to facilitate interchange, national or application-oriented standards may specify a standard repertoire of graphic characters which permit only a limited number of compos
45、ite graphic characters. Such limitations are considered fully compatible with ISO/IEC 646. B.2.4 Versions In a standard, one or more versions can be specified. It should be noted that a version is not a standard but only part of a standard. The standard itself consists of the CO set and the well-def
46、ined version or versions and a set of clauses as mentioned above. The definition of a version requires that the options mentioned in 8.1 be properly exercised. 14 ISO/IEC 646:1991 (E) Annex C (informative) Differences between the second edition (1983) and the present (third) edition of this Internat
47、ional Standard C.l The new text for the conformance clause adopted by JTCUSC2 for all code standards has been introduced. C.2 The wording of all definitions has been aligned with that of ISO/IEC 4873 and ISO/IEC 10538. C.3 In the GO set of the IRV the character DOLLAR SIGN replaces the character CUR
48、RENCY SIGN in position 2/4. Otherwise this GO set is unchanged. C.4 The requirements for the CO set have been relaxed. The sole requirement is that the CO set be a sub- set of the CO set of the second edition of this International Standard. This CO set is shown in normative annex A. For the definiti
49、ons of the 32 control characters reference is made to ISO/IEC 6429. As a consequence the Basic Code Table (table 4) and table 5 showing a version of ISO/IEC 646 with the GO set of the IRV do not show any specific control characters in columns 0 and 1. 15 ISOllEC 646:1991(E) UDC 681 .X04:681.327.1 Descriptors: data PrOCeSSing, information interchange, character sets, coded character sets, IS0 seven-bit codes, control characters, graphic characters. Price based on 15 pages
