Extended UNIX Code (EUC)

This is a fixed ISO 2022 configuration with G1 (and possibly G2 and/or G3) pre-defined for a particular locale. No designator sequences or locking shifts are used, and the 8-bit single shifts are used to access G2 and G3. Moreover, the glyphs of the 2-byte sets in G1 and G3 are assumed to be twice as wide as those of the 1-byte set in G2 (and the US-ASCII characters in G0). Thus the sets and their byte representations are as follows:

set 0: 00-7F
US-ASCII (narrow)
set 1: GR GR
2-byte characters (wide)
set 2: 8E GR
extra 1-byte set (narrow)
set 3: 8F GR GR
extra 2-byte set (wide)

Some examples:

SHIFT-GB
G1 = GB 2312-80
Chinese EUC
G1 = GB 2312-80, G2 = row 8 of GB 2312-80 (half width)
Japanese EUC
G1 = JIS X0208-1990, G2 = right half of JIS X0201-1976, G3 = JIS X0212-1990
Korean EUC
G1 = KSC 5601-1987

Somewhat different is

Taiwanese EUC
G1 = CNS 11643-1986 level 1, G2 = 3-byte form of CNS 11643-1986

Part of Notes on CJK Character Codes and Encodings.