TIS-620 is a conventionally structured Extended ASCII national character set that retains full compatibility with 7-bit ASCII and uses the 8-bit range hex A1 to FB for encoding the Thai alphabet.
Due to the complex combining nature of Thai vowels and diacritics, TIS-620 is intended for information interchange only, and an additional display engine is required to compose characters correctly.
A nearly identical version of TIS-620 has been adopted as ISO/IEC 8859-11 in 2001, the sole difference being that ISO/IEC 8859-11 defines hex A0 as a non-breaking space, while TIS-620 leaves it undefined but reserved.
The ISO/IEC 8859-11 set has also been registered as ISO-IR-166 by Ecma International, but this variation adds explicit escape codes for signaling the beginning and end of Thai character sequences.
Code values 00-1F, 7F, 80-9F, A0, DB-DE and FC-FF are not assigned to characters by TIS-620.