ISO 646
ISO 646 defines the so-called International Alphabet No. 5 ( International Alphabet No. 5 , IA5), a group of character sets for the transmission and storage of data . It largely corresponds to the (US-) ASCII character set .
history
IA5 was adopted in 1963 by ISO as standard IS 646 and at the same time by CCITT as recommendation V.3. The CCITT revised Recommendation V.3 in 1984 and passed it as T.50. T.50 received a revision in 1992, the character set of which was then called the International Reference Alphabet (IRA). IA1 is the Morse code , IA2 is the teletype character set encoded in 5 bits .
For the national versions, 12 positions in the character set are released for nationally defined characters. The German variant is specified in DIN 66003 and is registered as variant 21; it uses eight of the national positions for the paragraph symbol , large and small umlauts and the ß . These characters replace e.g. B. the square and curly brackets of ASCII. US-ASCII is the national version number 6 according to the standard, but in practice US-ASCII is the international version because of its support by computer manufacturers around the world. The almost never used official international version does not contain the dollar sign , as the Soviet Union would otherwise have refused to approve the standard.
Not all national variants achieved the same distribution; the Dutch variant, for example, does not contain any characters that are absolutely necessary for printing Dutch texts, which is why most computers sold in the Netherlands used the unchanged ASCII character set and a US keyboard layout.
The national versions in ISO 646 were from the 1980s in practice through the de facto standard of the 8-bit MS-DOS - code pages of the IBM PC and the achtbittigen also ISO 8859 replaced character sets - the latter are such . B. used in Linux and Microsoft Windows . Unlike the national versions of ISO 646, all of these standards are based on the unchanged ASCII character set. The additional characters required no longer replace ASCII characters, but are added to them. This made it easier to exchange data between computers in different countries; For programmers outside the USA, too, life became easier, as many of the US-ASCII characters released for replacement in the ISO-646 standard, which are partially or completely missing in the other ISO-646 variants, are often in many programming languages occurrence.
ISO 646 also forms the basis for the character coding in teletext .
In the meantime, these 8-bit character sets have to gradually give way to Unicode .
Note the relationship between the numbers in the ISO 646 standards for the IA5 and ISO 10646 for UCS and Unicode .
construction
IA5 largely corresponds to the US-American ASCII , but also serves as IRV (International Reference Version) for standardized national variants of the IA5. These national variants were often used on older computer systems (pre- PC ) to e.g. B. to display German umlauts . ISO 646 was e.g. B. on the Apple IIe and in CP / M computers the usual method of displaying non-English special characters.
Each character or control character in IA5 is coded with 7 bits just like in ASCII . The character set includes upper and lower case letters, digits, punctuation marks and characters in the lower 32 characters for controlling data communication or output devices.
| Character position: | 23 | 24 | 40 | 5B | 5C | 5D | 5E | 60 | 7B | 7C | 7D | 7E |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| ISO 646-IRV | # | ¤ | @ | [ | \ | ] | ^ | ` | { | | | } | ~ |
| Germany | # | $ | § | Ä | Ö | Ü | ^ | ` | Ä | ö | ü | ß |
| Switzerland | ù | $ | à | é | ç | ê | î | O | Ä | ö | ü | û |
| USA (ASCII) | # | $ | @ | [ | \ | ] | ^ | ` | { | | | } | ~ |
| Great Britain | £ | $ | @ | [ | \ | ] | ^ | ` | { | | | } | ~ |
| France | £ | $ | à | ° | ç | § | ^ | ` | é | ù | è | ¨ |
| Canada | # | $ | à | â | ç | ê | î | O | é | ù | è | û |
| Finland | # | $ | @ | Ä | Ö | Å | Ü | é | Ä | ö | å | ü |
| Norway | # | $ | @ | Æ | O | Å | ^ | ` | æ | O | å | ~ |
| Sweden | # | $ | É | Ä | Ö | Å | Ü | é | Ä | ö | å | ü |
| Italy | £ | $ | § | ° | ç | é | ^ | ù | à | O | ù | ì |
| Netherlands | £ | $ | ¾ | ÿ | ½ | | | ^ | ` | ¨ | ƒ | ¼ | ´ |
| Spain | £ | $ | § | ¡ | Ñ | ¿ | ^ | ` | ° | ñ | ç | ~ |
| Portugal | # | $ | @ | Ã | Ç | O | ^ | ` | ã | ç | O | ~ |
See also
Web links
- CCITT specification T.50 (English)