ISO/IEC 646:1991
(Main)Information technology — ISO 7-bit coded character set for information interchange
Information technology — ISO 7-bit coded character set for information interchange
Specifies a set of 128 control and graphic characters such as letters, digits and symbols with their coded representation. Applies to alphabets of the Latin script.
Technologies de l'information — Jeu ISO de caractères codés à 7 éléments pour l'échange d'information
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Standards Content (Sample)
INTERNATIONAL
STANDARD
Third edition
1991-12-15
Information technology - IS0 7-bit coded
character set for information interchange
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ISO/IEC 646:1991 (E)
Contents
Page
1
1 Scope
1
2 Conformance and implementation
1
2.1 Conformance
1
2.1.1 Conformance of information interchange
1
2.1.2 Conformance of devices
2
2.2 Implementation
2
3 Normative references
2
4 Definitions
2
4.1 active position
2
4.2 bit combination
2
4.3 character
2
4.4 character position
2
4.5 coded character set
3
4.6 coded-character-data-element (CC-data-element)
3
4.7 code extension
3
4.8 code table
3
4.9 control character
3
4.10 control function
3
4.11 device
3
4.12 escape sequence
3
4.13 Final Byte
3
4.14 graphic character
3
4.15 graphic symbol
.
3
4.16 repertoire
3
. 4.17 user
3
5 Notation, code table and names
3
5.1 Notation
4
5.2 Code table
4
5.3 Names
4
6 Specification of the coded character set
4
6.1 Structure
5
6.2 Control characters
0 ISO/IFc 1991
All rights reserved. No part of this publication may be reproduced or utilized in any form or by any
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wxiting from the publisher.
ISO/IEC Copyright Of&e l Case postale 56 l CH-1211 Gen&ve 20 l Switzerland
I?rintedin switiand
ii
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ISOLIEC 646:1991 (E)
6.3 Character SPACE
6.4 Graphic characters
6.4.1 Unique graphic character allocations
6.4.2 Alternative graphic character allocations
6.4.3 National or application-oriented graphic character allocations
6.5 Character DELETE 8
7 Composite graphic characters 8
8 Versions of the coded character set
8
8.1 General
8.2 International Reference Version (IRV) 9
8.3 National versions 9
8.4 Application-oriented versions 10
9 Identification of versions 10
9.1 Purpose and context of identification 10
9.2 Identification of a version 10
10 Explanation of Code tables No. 4 and No. 5 10
Annexes
13
A Specification of the CO set
B Guidelines for standards derived from ISO/IEC 646 14
C Differences between the second edition (1983) and the present (third) edition of this International
15
Standard
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ISO/IEC 646:1991 (E)
Foreword
IS0 (the International Organization for Standardization) and IEC (the
International Electrotechnical Commission) form the specialized system for
worldwide standardization. National bodies that are members of IS0 or
IEC participate in the development of International Standards through
technical committees established by the respective organization to deal with
particular fields of technical activity. IS0 and IEC technical committees
collaborate in fields of mutual interest. Other international organizations,
governmental and non-governmental, in liaison with IS0 and IEC, also
take part in the work.
In the field of information technology, IS0 and IEC have established a
joint technical committee, ISO/IEC JTC 1. Draft International Standards
adopted by the joint technical committee are circulated to national bodies
for voting. Publication as an International Standard requires approval by at
least 75 % of the national bodies casting a vote.
International Standard ISO/IEC 646 was prepared by Joint Technical
Information technology.
Committee ISO/IEC JTC 1,
This third edition cancels and replaces the second edition (IS0 646 : 1983)
which has been technically revised.
B
Annex A forms an integral part of this International Standard. Annexes
and C are for information only.
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INTERNATIONAL STANDARD ISO/IEC 646 : 1991 (E)
IS0 7-bit coded character set for
Information technology -
information interchange
1 scope
This International Standard 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 unchangeable, but provision is made for some flexibility to accommodate national and other
requirements.
This International Standard 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 application-oriented
versions. Furthermore it specifies the International Reference Version (IRV) in which such options have
been exercised.
This character set is primarily intended for the interchange of information among data processing systems
and associated equipment, and within data communication systems. The need for graphic characters and
control functions in data processing has also been taken into account in determining this character set.
This character set is applicable to alphabets of the Latin script.
This character set allows the use of control characters for code extension where its character set is
insufficient for particular applications. Procedures for the use of these control characters are specified in
IS0 2022.
The definitions of the control characters mentioned in this International Standard are specified in
IS0 6429. It is assumed that data associated with them are 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 treatment to ensure that they result in their desired function.
2 Conformance and implementation
2.1 Conformance
2.1.1 Conformance of information interchange
A coded-character-data-element (CC-data-element) within coded information for interchange is in
conformance with this International Standard if all the coded representations of characters within that CC-
data-element conform to the requirements of 8.1 of this International Standard.
A claim of conformance shall identify the version adopted in accordance with 8.2 to 8.4.
2.1.2 Conformance of devices
A device is in conformance with this International Standard if it conforms to the requirements of 2.1.2.1,
and either or both of 2.1.2.2 and 2.1.2.3 below. A claim of conformance shall identify the version adopted.
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ISO/IEC 646:1991 (E)
2.1.2.1 Device description
A device that conforms to this International Standard shall be the subject of a description that identifies
the means by which the user may supply characters to the device, or may recognize them when they are
made available to him, as specified respectively in 2.1.2.2 and 2.1.2.3.
2.1.2.2 Originating devices
An originating device shall allow its user to supply any sequence of characters from the version
and shall be capable 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 characters
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 include 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 devices and computers) or by means of data transmission equipment.
The implementation of this coded physical media and for transmission, taking into account
character set in
the need for error checking, is the International Standards.
subject of other
3 Normative references
The following standards contain provisions which, through reference in this text, constitute provisions of
this International Standard. At the time of publication, the editions indicated were valid. Ail standards are
subject to revision, and parties to agreements based on this International Standard are encouraged to
investigate the possibility of applying the most recent editions of the standards listed below. Members of
IEC and IS0 maintain registers of currently valid International Standards.
IS0 7-bit and S-bit coded character sets - Code extension
IS0 2022 : 1986, Information processing -
. techniques.
ISO/IEC 6429 3, Information processing - Control functions for 7-bit and 8-bit coded character sets.
4 Definitions
For the purpose of this International Standard the following definitions apply.
to image the graphic symbol representing the next
4.1 active position : The character position which is
function is to be executed.
graphic character or relative to which the next control
NOTE 1 - In general, the active position is indicated in a display by a cursor.
4.2 bit combination : An ordered set of bits used for the representation of characters.
4.3 character : A member of a set of elements used for the organization, control or representation of data.
4.4 character position : The portion of a display that is imaging or is capable of imaging a graphic symbol.
4.5 coded character set; 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 bit combinations.
1) To be published.
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ISO/IEC 646:1991 (E)
: An element of interchanged information that is
4.6 coded-character-data-element (CC-data-element)
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 Systems interconnection (IS0
7498), 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-element will
form all or part of the information that corresponds to’ the user data, and not that recorded during formatting and
initialization.
encoding of characters that are not included in the character
4.7 code extension : The techniques for the
of a given code.
set
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 the recording, processing, transmission, or interpretation of
data, and that has a coded representation consisting of one or more bit combinations.
and/or receive, coded .
4.11 device : A component of information processing equipment which can transmit,
information within CC-data-elements.
NOTE 4 - It may in the conventional or a such as an application program or
be an input/output device sense,
Pro==
gateway function.
: A string of bit combinations that is used for control purposes in code extension
4.12 escape sequence
procedures. The first 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 displayed, 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 coded character set.
4.17 user : A person or other entity that invokes the services provided by a device.
program if the “device” is a code convertor
NOTE 5 - This entity may be a process such as an application
gateway function, for example.
available to him, may be in the form of local to the
NOTE b- The characters, as supplied by the user or made
.2 above is satisfied.
device, or of non -conventional visible representations, provided that 2.1
5 Notation, code table and names
5.1 Notation
.
The bits of the bit combinations of the 7-bit code are identified by b, bb, bg, b4, b3, b2 and bl, where b7 is
the highest-order, or most-significant, bit and bl is the lowest-order, or least-significant, bit.
in the range 0 to 127 in binary notation by
The bit combinations may be interpreted to represent integers
attributing the following weights to the individual bits:
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ISOAEC 646:1991 (E)
\
Bd . 0
0
b7 b6 b5 b4 b3 b2 bl
1
\
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 combinations consisting of the bits b7 to bl is as follows:
- x is the number represented by b7, bb and b5 where these bits are given the weights 4, 2 and 1
respectively;
- y is the number represented by b4, b3, b2 and bl where these bits are given the weights 8, 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 to 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 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 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 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 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 &led character set
6.1 Structure
The coded character set of this Jnternational 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).
4
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ISO/IEC 646:lWl (E)
GO
Figure 1 - Structure 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 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, 6.4.2 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 graphic character allocations
A unique graphic character is allocated to each of the 82 bit combinations 2/l, 212, 2/5 to 3/U, 4/I to S/10,
505 and 6/l to 7/10. These graphic characters are specified in table 1.
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ISO/IEC 646:1991 (E)
Table 1 - Unique graphic character allocations
Graphic Coded
Name
Symbol representation
,
!
EXCLAMATION MARK
211
II
QUOTATION MARK
m
% PERCENT SIGN
m
&
AMPERSAND
2/6
I
APOSTROPHE
2/7
LEFT PARENTHESIS
( 2/a
RIGHT PARENTHESIS
> 2/g
*
ASTERISK 2/10
+
PLUS SIGN 2/11
COMMA
2112
9
HYPHEN-MINUS
2/13
0 FULL STOP 2114
SOLIDUS 2/15
/
0
DIGIT ZERO
3/o
1 DIGIT ONE
311
2 DIGIT TWO
3/2
3
DIGIT THREE
313
4
DIGIT FOUR
w
5 DIGIT FIVE
3/5
6 DIGIT SIX
3/6
7 DIGI
...
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