The Vietnamese Standard Code for Information Interchange (VISCII) is a character set comprising the Vietnamese alphabet, punctuation, and other graphemes. Vietnamese requires slightly too many (134) letter/diacritic combinations to make a traditional extended ASCII character set for it. There are essentially 3 possible solutions to this.

1. Use a variable width encoding
2. Use combining diacritical marks, as Windows-1258 does
3. Replace something from ASCII

VISCII went for the last option, replacing 6 of the least problematic (e.g., least likely to be recognised by an application and acted on specially) C0 control codes (STX, ENQ, ACK, DC4, EM, and RS) with 6 of the least used uppercase letter/diacritic combinations. While this may cause issues with some programs in handling VISCII text if they use those control codes, it creates fewer complications than either of the other two solutions. However, it leaves absolutely no space available for things other than accented letters such as symbols, superscripted numbers, curved quotes, proper dashes, etc.

VISCII, along with other Vietnamese-specific character sets, fell out of usage with the adoption of Unicode.

Codepage layout

External links

• RFC 1456 - Conventions for Encoding the Vietnamese Language
• Vietnamese-Standard Working Group
• Viet-Std Report 1992
• AnGiang Software

Character sets | Vietnamese language

Vietnamese Standard Code for Information Interchange | VISCII | VISCII