Revision as of 11:10, 20 August 2019 by HarJIT(talk | contribs)(Easier understood in terms of what support each level adds, not removes: also, VSCII clearly adds more than 128 chars (although the additional 12 obviously remove C0 controls); also, Đ doesn't have a decomposition and so isn't really "precomposed".)
VSCII (Vietnamese Standard Code for Information Interchange) also known as TCVN 5712:1993 and ISO-IR-180,[2] is a set of three Vietnamese national standardcharacter encodings for using the Vietnamese language with computers, developed by the TCVN Technical Committee on Information Technology (TCVN/TC1) and first adopted in 1993.[3] It should not be confused with the similarly-named unofficial VISCII encoding.
Unicode and the Windows-1258 code page are now used for virtually all Vietnamese computer data, but legacy VSCII and VISCII files may need conversion.
VSCII-3, also known as TCVN 5712-3 and VN3, includes the fewest assignments. It is an extended ASCII, because it keeps all 128 codes of ASCII unmodified. It does not re-assign any of the C0 and C1 control codes. Compared to ASCII, it adds 75 characters:
VSCII-2, also known as TCVN 5712-2 and VN2, is a superset of VSCII-3. It is an extended ASCII, because it keeps all 128 codes of ASCII unmodified. It does not re-assign any of the C0 and C1 control codes, making it conformant with ISO 2022 as a 96-set.[3] Compared to VSCII-3, it adds (for a total of 96 non-ASCII characters):
16 more pre-composed uppercase letters (for a total of 23 non-ASCII uppercase letters)
5 combining diacritics, allowing other uppercase letter diacritic combinations to be represented
VSCII-1, also known as TCVN 5712-1 and VN1, is an extension of VSCII-2, and is a modified ASCII, since it replaces 12 of the 33 control characters with precomposed characters. Compared to VSCII-2, it (for a total of 140 non-ASCII characters, or 134 non-ASCII letters):
Adds 44 more pre-composed uppercase letters, bringing them to the same count as the lowercase
Does this by replacing 12 ASCII control characters and allocating 32 graphical characters to the C1 control area, breaking ISO 2022 compatibility
Conversion from VSCII-3 to VSCII-2 or VSCII-1 and conversion from VSCII-2 to VSCII-1 are not necessary, but can result in smaller files.
Conversion from VSCII-1 to VSCII-2 or VSCII-3 and conversion from VSCII-2 to VSCII-3 require expansion of some pre-composed characters.
