ISO/IEC 6937

ISO/IEC 6937:2001, Information technology — Coded graphic character set for text communication — Latin alphabet, is a multibyte extension of ASCII, or rather of ISO/IEC 646-IRV. It was developed in common with ITU-T (then 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. Only certain combinations of lead byte and follow byte are allowed, and there are some exceptions to the lead byte interpretation for some follow bytes. However, that no combining characters at all are encoded in ISO/IEC 6937. But one can represent some free-standing diacritics, often by letting the follow byte have the code for ASCII space.

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 Latin alphabet. Non-Latin European characters, such as Cyrillic and Greek, are not included in the standard. Also, some diacritics used with the Latin alphabet like the Romanian 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.

The ISO/IEC 2022 escape sequence to specify the right-hand side of the ISO/IEC 6937 character set is ESC - R (hex 1B 2D 52).^[1]

Single byte characters

The primary set of ISO6937/2 is based on ISO 646-IRV (characters 0x00..0x7F) before the ISO/IEC 646:1991 revision, that is with character 0x24 still denoted as a "international currency sign" (¤) instead of the dollar sign ($):

	!"#¤%&'()*+,-./0123456789:;<=>?@
	ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]^_`
	abcdefghijklmnopqrstuvwxyz{|}

The supplementary set (characters 0x80..0xFF) contains a selection of spacing and non-spacing graphic characters, additional symbols and some locations reserved for future standardisation.

Two byte characters

The characters, which are not represented in the primary set, are coded on 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

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
DoubleAcute	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 are only indicative of which “accent” is usually intended by that lead byte. ISO/IEC 6937 does not encode any combining characters whatsoever. Instead, there is an explicit list of precomposed characters that are encoded.

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.

Unicode distinguishes 0xE2 into uppercase Eth and D with stroke, which usually look different for the lowercase letters (0xF2 and 0xF3).

Legend:

Alphabetic   Control character   Numeric digit   Punctuation

Extended punctuation   Graphic character   International   Undefined

ISO/IEC 6937 (Latin)

	_0	_1	_2	_3	_4	_5	_6	_7	_8	_9	_A	_B	_C	_D	_E	_F
0_	0	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15
1_	16	17	18	19	21	21	22	23	24	25	26	27	28	29	30	31
2_	SP 0020 32	! 0021 33	" 0022 34	# 0023 35	$ 0024 36	% 0025 37	& 0026 38	' 0027 39	( 0028 40	) 0029 41	* 002A 42	+ 002B 43	, 002C 44	- 002D 45	. 002E 46	/ 002F 47
3_	0 0030 48	1 0031 49	2 0032 50	3 0033 51	4 0034 52	5 0035 53	6 0036 54	7 0037 55	8 0038 56	9 0039 57	: 003A 58	; 003B 59	< 003C 60	= 003D 61	> 003E 62	? 003F 63
4_	@ 0040 64	A 0041 65	B 0042 66	C 0043 67	D 0044 68	E 0045 69	F 0046 70	G 0047 71	H 0048 72	I 0049 73	J 004A 74	K 004B 75	L 004C 76	M 004D 77	N 004E 78	O 004F 79
5_	P 0050 80	Q 0051 81	R 0052 82	S 0053 83	T 0054 84	U 0055 85	V 0056 86	W 0057 87	X 0058 88	Y 0059 89	Z 005A 90	[ 005B 91	\ 005C 92	] 005D 93	^ 005E 94	_ 005F 95
6_	` 0060 96	a 0061 97	b 0062 98	c 0063 99	d 0064 100	e 0065 101	f 0066 102	g 0067 103	h 0068 104	i 0069 105	j 006A 106	k 006B 107	l 006C 108	m 006D 109	n 006E 110	o 006F 111
7_	p 0070 112	q 0071 113	r 0072 114	s 0073 115	t 0074 116	u 0075 117	v 0076 118	w 0077 119	x 0078 120	y 0079 121	z 007A 122	{ 007B 123	| 007C 124	} 007D 125	~ 007E 126	DEL 007F 127
8_	128	129	130	131	132	133	134	135	136	137	138	139	140	141	142	143
9_	144	145	146	147	148	149	150	151	152	153	154	155	156	157	158	159
A_	NBSP 00A0 160	¡ 00A1 161	¢ 00A2 162	£ 00A3 163	164	¥ 00A5 165	166	§ 00A7 167	¤ 00A4 168	‘ 2018 169	“ 201C 170	« 00AB 171	← 2190 172	↑ 2191 173	→ 2192 174	↓ 2193 175
B_	° 00B0 176	± 00B1 177	² 00B2 178	³ 00B3 179	× 00D7 180	µ 00B5 181	¶ 00B6 182	· 00B7 183	÷ 00F7 184	’ 2019 185	” 201D 186	» 00BB 187	¼ 00BC 188	½ 00BD 189	¾ 00BE 190	¿ 00BF 191
C_	192	̀ 0300 193	́ 0301 194	̂ 0302 195	̃ 0303 196	̄ 0304 197	̆ 0306 198	̇ 0307 199	̈ 0308 200	201	̊ 030A 202	̧ 0327 203	204	̋ 030B 205	̨ 0328 206	̌ 030C 207
D_	― 2015 208	¹ 00B9 209	® 00AE 210	© 00A9 211	™ 2122 212	♪ 266A 213	¬ 00AC 214	¦ 00A6 215	216	217	218	219	⅛ 215B 220	⅜ 215C 221	⅝ 215D 222	⅞ 215E 223
E_	Ω 2126 224	Æ 00C6 225	Đ 0110 226	ª 00AA 227	Ħ 0126 228	229	IJ 0132 230	Ŀ 013F 231	Ł 0141 232	Ø 00D8 233	Œ 0152 234	º 00BA 235	Þ 00DE 236	Ŧ 0166 237	Ŋ 014A 238	ʼn 0149 239
F_	ĸ 0138 240	æ 00E6 241	đ 0111 242	ð 00F0 243	ħ 0127 244	ı 0131 245	ij 0133 246	ŀ 0140 247	ł 0142 248	ø 00F8 249	œ 0153 250	ß 00DF 251	þ 00FE 252	ŧ 0167 253	ŋ 014B 254	SHY 00AD 255
	_0	_1	_2	_3	_4	_5	_6	_7	_8	_9	_A	_B	_C	_D	_E	_F

References

1. Supplementary Set of ISO/IEC 6937:1992 The high-ASCII half of the character set. (The left-hand side is U.S. ASCII.)