T.51/ISO/IEC 6937

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T.51
Latin based coded character sets for telematic services
StatusIn force
Year started1984
Latest version(09/92)
September 1992
OrganizationITU-T
CommitteeStudy Group VIII
Related standardsT.61, ETS 300 706, ISO/IEC 10367, ISO/IEC 2022, ISO 5426
Domainencoding
LicenseFreely available
Websitehttps://www.itu.int/rec/T-REC-T.51
T.51
Alias(es)
  • Code page 20269
  • ISO-IR
    -90 (old)
  • ISO-IR-142 (old)
  • ISO-IR-156
Standard
Based onITU T.61
Other related encoding(s)

T.51 / ISO/IEC 6937:2001, Information technology — Coded graphic character set for text communication — Latin alphabet, is a multibyte extension of

CCITT) for telematic services under the name of T.51, and first became an ISO standard in 1983. Certain byte codes are used as lead bytes for letters with diacritics
(accents). The value of the lead byte often indicates which diacritic that the letter has, and the follow byte then has the ASCII-value for the letter that the diacritic is on.

ISO/IEC 6937's architects were Hugh McGregor Ross, Peter Fenwick, Bernard Marti and Loek Zeckendorf.

ISO6937/2 defines 327 characters found in modern European languages using the

comma
are not included, using cedilla instead as no distinction between cedilla and comma below was made at the time.

IANA has registered the charset names ISO_6937-2-25 and ISO_6937-2-add for two (older) versions of this standard (plus control codes). But in practice this character encoding is unused on the Internet.

Single byte characters

The primary set (first half) originally followed

international currency sign" (¤) instead of the dollar sign ($). The 1992 edition of ITU T.51 permits existing CCITT services to continue to interpret 0x24 as the international currency sign, but stipulates that new telecommunication applications should use it for the dollar sign (i.e. following the current ISO 646-IRV), and instead represent the international currency sign using the supplementary set.[2]

The supplementary set (second half) contains a selection of spacing and non-spacing graphic characters, additional symbols and some locations reserved for future standardisation.

Both of these are

ISO-IR-106.[4]

The ISO/IEC 2022 escape sequence to designate the supplementary set of ISO/IEC 6937 as the G2 set is ESC . R (hex 1B 2E 52).[2][5][6] The older ISO 6937/2:1983 supplementary set is registered as a 94-code set, and designated to G2 with ESC * l (hex 1B 2A 6C).[5][7]

Two byte characters

Accented letters which are not allocated single codes in the primary or supplementary set are coded using two bytes. The first byte, the "non spacing diacritical mark", is followed by a letter from the base set e.g.: 

small e with acute accent (é) = [Acute]+e

The ITU T.51 standard allocates column 4 of the supplementary set (i.e.

ISO/IEC 10646 character names. The isolated nonspacing bytes are not included in this repertoire, although spacing variants of the diacritics not otherwise present in ASCII are included, with the ASCII space being the trail byte.[5][8]
Hence, only certain combinations of lead byte and follow byte conform to the ISO/IEC standard.

This repertoire is also affixed to the ITU version of the specification as Annex A, although the ITU version does not reference it from the main text. It is described as a "unified superset" of the Latin-script character repertoires.

Latin-2 and supplementary Latin sets are used.[5]

This system also differs from the Unicode combining character system in that the diacritic code precedes the letter (as opposed to following it), making it more similar to ANSEL.

A little anomaly is that Latin Small Letter G with Cedilla is coded as if it were with an acute accent, that is, with a 0xC2 lead byte, since due to its descender interfering with a cedilla, the lowercase letter is usually with turned comma above: Ģ ģ.

In total 13 diacritical marks can be followed by the selected characters from the primary set:

Accent Code Second character Result
Grave 0xC1 AEIOUaeiou ÀÈÌÒÙàèìòù
Acute 0xC2 ACEILNORSUYZacegilnorsuyz ÁĆÉÍĹŃÓŔŚÚÝŹáćéģíĺńóŕśúýź
Circumflex 0xC3 ACEGHIJOSUWYaceghijosuwy ÂĈÊĜĤÎĴÔŜÛŴŶâĉêĝĥîĵôŝûŵŷ
Tilde 0xC4 AINOUainou ÃĨÑÕŨãĩñõũ
Macron 0xC5 AEIOUaeiou ĀĒĪŌŪāēīōū
Breve 0xC6 AGUagu ĂĞŬăğŭ
Dot 0xC7 CEGIZcegz ĊĖĠİŻċėġż
Umlaut or diæresis 0xC8 AEIOUYaeiouy ÄËÏÖÜŸäëïöüÿ
Ring 0xCA AUau ÅŮåů
Cedilla 0xCB CGKLNRSTcklnrst ÇĢĶĻŅŖŞŢçķļņŗşţ
Double Acute 0xCD OUou ŐŰőű
Ogonek 0xCE AEIUaeiu ĄĘĮŲąęįų
Caron 0xCF CDELNRSTZcdelnrstz ČĎĚĽŇŘŠŤŽčďěľňřšťž

Codepage layout

The reference to combining characters in the U+0300—U+036F range for the codes in the range 0xC1—0xCF below is subject to the caveats mentioned above; they cannot simply be mapped to the codepoints listed. Also, Unicode distinguishes 0xE2 into uppercase D with stroke and uppercase Eth, which usually look different for the lowercase letters (0xF2 and 0xF3).

The older 1988 edition of ITU T.51 defined two versions of the supplementary set, with the first version lacking the

¦) present in the second version. The first version was defined as an extension of the T.61 supplementary set, and the second version as an extension of the first version.[9] The current (1992) edition only includes the second version, deprecates certain characters, and updates the primary set to the current ISO-646-IRV (ASCII), although existing telematic services are permitted to retain the older behaviour.[2]

ISO/IEC 6937 or ITU T.51 (Latin)
0 1 2 3 4 5 6 7 8 9 A B C D E F
0x
1x
2x  
SP
  		! " #
¤[a]
 % & ' ( ) * +
,
 - . /
3x
0
1
2
3
4
5
6
7
8
9
 : ;
<
=
>
 ?
4x
@
 A B C D E F G H I J K L M N O
5x P Q R S T U V W X Y Z
[
 \
]
 ^ _
6x ` a b c d e f g h i j k l m n o
7x p q r s t u v w x y z { | } ~
8x
9x
Ax NBSP ¡ ¢ £ $[b]
¥
 #[b] §
¤
‘
“
«
 ← ↑ → ↓
Bx
°
±
²
³
×
µ
·
÷
’
”
»
¼
 ½
¾
¿
Cx ◌̀ ◌́ ◌̂ ◌̃ ◌̄ ◌̆ ◌̇ ◌̈ ◌̊ ◌̧
◌̲[c]
 ◌̋ ◌̨ ◌̌
Dx
―
¹
®
©
™
♪
¬
¦
⅛
⅜
⅝
⅞
Ex Ω Æ
Ð
ª
Ħ
 [d]
IJ
Ŀ
 Ł Ø Œ
º
Þ
Ŧ
Ŋ
ʼn
Fx
ĸ
 æ
đ
ð
ħ
 ı
ij
ŀ
 ł ø œ ß
þ
ŧ
ŋ
 SHY
  Differences from T.61

Videotex version

Main article: Videotex character set

The versions of the supplementary set used by the ITU T.101 standard for Videotex are based on the first supplementary set of the 1988 edition of T.51.

The default G2 set for Data Syntax 2 adds a

΅ at 0xC0, for combination with codes from a Greek primary set.[10]

The supplementary set for Data Syntax 3 adds non-spacing marks for a "vector overbar" and solidus and several semigraphic characters.[11]

ETS 300 706 version

The ETS 300 706 standard for

US-ASCII or BS_viewdata
. This version is shown in the chart below.

World System Teletext, Latin G2 Set (ETS 300 706:1997)[12]
0 1 2 3 4 5 6 7 8 9 A B C D E F
Ax  SP  ¡ ¢ £ $
¥
 # §
¤
‘
“
«
 ← ↑ → ↓
Bx
°
±
²
³
×
µ
·
÷
’
”
»
¼
 ½
¾
¿
Cx ◌̀ ◌́ ◌̂ ◌̃ ◌̄ ◌̆ ◌̇ ◌̈ ̣◌̣ ◌̊ ◌̧
◌̲
 ◌̋ ◌̨ ◌̌
Dx
―
¹
®
©
™
♪
 ₠ ‰
α
⅛
⅜
⅝
⅞
Ex Ω Æ
Ð
ª
Ħ
IJ
Ŀ
 Ł Ø Œ
º
Þ
Ŧ
Ŋ
ʼn
Fx
ĸ
 æ
đ
ð
ħ
 ı
ij
ŀ
 ł ø œ ß
þ
ŧ
ŋ
 ■
  Differences from T.51

See also

Footnotes

  1. ^ Continued use for ¤ permitted for existing CCITT services only.[2]
  2. ^ a b Permitted for existing CCITT services only, otherwise the ASCII representation should be used.[2]
  3. ANSI escape sequences, although it does mention that it should be correctly interpreted when received by applicable systems.[2] Previous editions of the ISO/IEC version of the standard also allowed combining this code with any character in the defined repertoire,[7] whereas more recent revisions do not include this code.[5]
  4. ^ An early draft placed ȷ in this position.

References

  1. ^ "T.51 : Latin based coded character sets for telematic services". www.itu.int. Archived from the original on 2019-10-08. Retrieved 2019-11-14.
  2. ^ a b c d e f g h CCITT (1992-09-18). Latin based coded character sets for telematic services (1992 ed.). Recommendation T.51.
  3. ^ ITU-T (1995-08-11). Recommendation T.51 (1992) Amendment 1.
  4. ISO-IR
    -106.
  5. ^ a b c d e ISO/IEC JTC 1/SC 2/WG 3 (1998-04-15). WD 6937, Coded graphic character set for text communication - Latin alphabet (PDF). JTC1/SC2/N454.{{citation}}: CS1 maint: numeric names: authors list (link)
  6. ISO-IR-156.{{citation}}: CS1 maint: numeric names: authors list (link) (The left-hand side is US-ASCII
    .)
  7. ^
    ISO-IR-90.{{citation}}: CS1 maint: numeric names: authors list (link
    )
  8. ISBN 978-1-4200-4067-8
    .
  9. ^ a b CCITT (1988). Coded character sets for telematic services (1988 ed.). Recommendation T.51.
  10. ISO-IR
    -70.
  11. ISO-IR
    -128.
  12. ^
    ETSI (1997). "15.6.3 Latin G2 Set". Enhanced Teletext specification (PDF)
    (PDF). p. 116. ETS 300 706.

External links
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