ANSI INCITS ISO IEC 646-1991 Information Technology - ISO 7-Bit Coded Character Set for Information Interchange《信息技术.信息交换用ISO 7位编码字符集》.pdf
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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 Copyright American National Standards Institute Provided by IHS under license with ANSINot for ResaleNo reproduction or networking permitted without license from IHS-,-,-4.6 coded-character-data-element (CC-data-element) : An ele
3、ment 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 identified standards for coded character sets. NOTE 2 - In a communication environment according to the Reference Model for Open Sys
4、tems 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 that International Standard. NOTE 3 - When information interchange is accomplished by means of interchangeable media, a CC-data-el
5、ement 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 not included in the character set of a given code. 4.8 code table : A table showin
6、g 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 the recording, processing, transmission, or interpretation of data, and that
7、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, coded information within CC-data-elements. NOTE 4 - It may be an input/output device in the conventional sense, or a process such a
8、s 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 first of these bit combinations represents the control function ESCAPE. 4.13 Final Byte : The bit combination that terminates an escap
9、e 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 displayed, and that has a coded representation consisting of one or more bit combinations. 4.15 graphic symbol : A visual represent
10、ation 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 coded character set. 4.17 user : A person or other entity that invokes the services provided by a device. NOTE 5 - This entity may
11、 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 made available to him, may be in the device, or of non-conventional visible representations, provided that 2.1.2 above is satisfied
12、. 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 bl, where is the highest-order, or most-significant, bit and bl is the lowest-order, or least-significant, bit. The bit combination
13、s may be interpreted to represent integers in the range 0 to 127 in binary notation by attributing the following weights to the individual bits: Copyright American National Standards Institute Provided by IHS under license with ANSINot for ResaleNo reproduction or networking permitted without licens
14、e from IHS-,-,-ISO/IEC 646:1991 (E) Bit : 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 no
15、tations of the form x/y and the bit combinations 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,
16、4, 2 and 1 respectively. The notations of 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 t
17、o 7 and the rows 0 to 15. The code table 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
18、form x/y, is the same as that of the corresponding 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 c
19、onvention, 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 that the acronyms and this convention be retained in all translations of the text. The names chosen to denote graphic characters a
20、re intended to reflect their customary meaning. 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
21、6.1 Structure The coded character set of 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). Copyrig
22、ht American National Standards Institute Provided by IHS under license with ANSINot for ResaleNo reproduction or networking permitted without license from IHS-,-,-ISO/IEC 646:1991 (E) GO Ii= DEI Figure 1 - Structure of the 7-bit coded character set 6.2 Control characters The control characters of th
23、e 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 character, it has a visual representation consisting of the absence of a graphic symbol. 6
24、.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, they cause the active position to advance by one character position. 6.4.1 Unique graphi
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