1、INTERNATIONAL STANDARD ISOllEC 4873 Third edition 1991-12-15 Information technology - IS0 8-bit code for information interchange - Structure and rules for implementation Technologies de /information - Code IS0 5 8 code : A set of unambiguous rules that establishes a character set and the one-to- one
2、 relationship between the characters of the set and their bit combinations. 4.8 code extension : The techniques for the encoding of characters that are not included in the character set of a given code. 4.9 code table : A table showing the character allocated to each bit combination in a code. 4.10
3、control character : A control function the coded representation of which consists of a single bit combination. 4.11 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 combinat
4、ions. 4.12 device : A component of information processing equipment which can transmit, and/or receive, coded information within CC-data-elements. NOTE It may be an input/output device in the conventional sense, or a process such as an application program or gateway function. 4.13 escape sequence :
5、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. 4.14 Final Byte : The bit combination that terminates an escape sequence or a control sequence. 4.15 graphic character : A characte
6、r, 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. 4.16 graphic symbol : A visual representation of a graphic character or of a control function. 4.17 repertoir
7、e : A specified set of characters that are represented by means of one or more bit combinations of a coded character set. 4.18 user : A person or other entity that invokes the services provided by a device. NOTES I. This entity may be a process such as an application program if the “device” is a cod
8、e convertor or a gateway function, for example. 2. The characters, as supplied by the user or made available to him, may be in the form of codes local to 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
9、The bits of the bit combinations of the 8-bit code are identified by bs, b7, bh, bg, b4, b3, b2 and br, where bx is the highest-order, or most-significant bit, and br is the lowest-order, or least-significant, bit. The bit combinations may be interpr-eted to represent integers in the range 0 to 255
10、in binary notation by attributing the following weights to the individual bits: 3 ISO/IEC 4873:1991 (E) Bit b8 b7 b6 hi b4 b3 b2 bl Weight 128 64 32 16 8 4 2 1 In this International Standard, the bit combinations are identified by notations of the form xx/yy, where xx and yy are numbers in the range
11、 00 to 15. The correspondence between the notations of the form xx/yy and the bit combinations consisting of the bits bg to br, is as follows: - xx is the number represented by bg, b7, bb and b5 where these bits are given the weights 8, 4, 2 and I respectively; - yy is the number represented by bq,
12、bj, b2 and bt where these bits are given the weights 8, 4, 2 and 1 respectively. The notations of the form xx/yy are the same as the ones used to identify code table positions, where xx is the column number and yy is the row number (see 5.2). 5.2 Code table An 8-bit code table consists of 256 positi
13、ons arranged in 16 columns and 16 rows. The columns and rows are numbered 00 to 15. The code table positions are identified by notations of the form xxlyy, where xx is the column number and yy is the row number. The positions of the code table are in one-to-one correspondence with the bit combinatio
14、ns of the code. The notation of a code table position, of the form xx/yy, 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 control characters and for the characters SPACE and D
15、ELETE, and a graphic symbol for each graphic character. By convention, only capital letters, and hyphen are used for writing the names of the characters. For acronyms only capital letters, space and digit are used. It is intended that the acronyms and this convention be retained in all translations
16、of the text. The names chosen to denote graphic characters are 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 charact
17、ers when imaged. 6 Structure of the &bit code 6.1 Elements of the g-bit code The g-bit code consists of the following parts (see figure 1). 4 A CO set A set of up to 30 control characters represented by bit combinations OO/OO to 01/15, except OO/l4 and OO/l5 which shall be unused. b) The character SPACE A graphic character represented by bit combination 02/00. cl A GO set A set of 94 graphic characters represented by bit combinations 02/01 to 07/14. 4
