The Vietnamese Standard Code for Information Interchange (VISCII) is a character set comprising the Vietnamese alphabet

Vietnamese alphabet

The Vietnamese alphabet, called Chữ Quốc Ngữ , usually shortened to Quốc Ngữ , is the modern writing system for the Vietnamese language...

, punctuation

Punctuation

Punctuation marks are symbols that indicate the structure and organization of written language, as well as intonation and pauses to be observed when reading aloud.In written English, punctuation is vital to disambiguate the meaning of sentences...

, and other graphemes. Vietnamese requires slightly too many (134) letter/diacritic combinations to make a traditional extended ASCII

Extended ASCII

The term extended ASCII describes eight-bit or larger character encodings that include the standard seven-bit ASCII characters as well as others...

 character set for it. There are essentially 3 possible solutions to this.

1. Use a variable width encoding
2. Use combining diacritical marks
   Combining character
   In digital typography, combining characters are characters that are intended to modify other characters. The most common combining characters in the Latin script are the combining diacritical marks ....
   
   , as Windows-1258
   Windows-1258
   Windows-1258 is a codepage used in Microsoft Windows to represent Vietnamese texts. It makes use of combining diacritical marks. Windows-1258 is not compatible with VISCII...
   
    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

C0 and C1 control codes

Most character encodings, in addition to representing printable characters, may also represent additional information about the text, such as the position of a cursor, an instruction to start a new line, or a message that the text has been received...

 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.

It was developed in 1992 by the Vietnamese Standardization Group (Viet-Std Group) from the TriChlor group in California

California

California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...

 and is officially registered as ISO-IR-180. VISCII, along with other Vietnamese-specific character sets, fell out of usage with the adoption of Unicode

Unicode

Unicode is a computing industry standard for the consistent encoding, representation and handling of text expressed in most of the world's writing systems...

.

Code page layout

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External links

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