Chapter 4. Coded Character Sets And Encodings in the World

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4.3 ISO 2022

Using ASCII and ISO 646, we can use 94 characters at most. Using ISO 8859, the number includes

to 190 (= 94 + 96). However, we may want to use much more characters. Or, we may want to use

some, not one, of these character sets. One of the answer is ISO 2022.

ISO 2022 is an international standard of CES. ISO 2022 determines a few requirement for CCS to

be a member of ISO 2022 based encodings. It also defines a very extensive (and complex) rules

to combine these CCS into one encoding. Many encodings such as EUC *, ISO 2022 *, compound

text,

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and so on can be regarded as subsets of ISO 2022. ISO 2022 is so complex that you may be

not able to understand this. It is OK; What is important here is the concept of ISO 2022 of building

an encoding by switching various (ISO 2022 compliant) coded character sets.

The sixth edition of ECMA 35 is fully identical with ISO 2022:1994 and you can find the official

document at

http://www.ecma.ch/ecma1/stand/ECMA 035.HTM

.

ISO 2022 has two versions of 7bit and 8bit. At first 8bit version is explained. 7bit version is a

subset of 8bit version.

The 8bit code space is divided into four regions,

  0x00   0x1f: C0 (Control Characters 0),

  0x20   0x7f: GL (Graphic Characters Left),

  0x80   0x9f: C1 (Control Characters 1), and

  0xa0   0xff: GR (Graphic Characters Right).

GL and GR is the spaces where (printable) character sets are mapped.

Next, all character sets, for example, ASCII, ISO 646 UK, and JIS X 0208, are classified into follow 

ing four categories,

  (1) character set with 1 byte 94 character,

  (2) character set with 1 byte 96 character,

  (3) character set with multibyte 94 character, and

  (4) character set with multibyte 96 character.

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Compound text is a standard for text exchange between X clients.