The National Replacement Character Set (NRCS) was a feature supported by later models of Digital's (DEC)

computer terminal A computer terminal is an electronic or electromechanical hardware device that can be used for entering data into, and transcribing data from, a computer or a computing system. The teletype was an example of an early-day hard-copy terminal and ...

systems, starting with the VT200 series in 1983. NRCS allowed individual characters from one

character set Character encoding is the process of assigning numbers to graphical characters, especially the written characters of human language, allowing them to be stored, transmitted, and transformed using digital computers. The numerical values tha ...

to be replaced by one from another set, allowing the construction of different character sets on the fly. It was used to customize the character set to different local languages, without having to change the terminal's

ROM Rom, or ROM may refer to: Biomechanics and medicine * Risk of mortality, a medical classification to estimate the likelihood of death for a patient * Rupture of membranes, a term used during pregnancy to describe a rupture of the amniotic sac * ...

for different countries, or alternately, include many different sets in a larger ROM. Many 3rd party terminals and

terminal emulator A terminal emulator, or terminal application, is a computer program that emulates a video terminal within some other display architecture. Though typically synonymous with a shell or text terminal, the term ''terminal'' covers all remote term ...

s supporting VT200 codes also supported NRCS.

Description

ASCII ASCII ( ), abbreviated from American Standard Code for Information Interchange, is a character encoding standard for electronic communication. ASCII codes represent text in computers, telecommunications equipment, and other devices. Because ...

is a 7-bit standard, allowing a total of 128 characters in the character set. Some of these are reserved as

control character In computing and telecommunication, a control character or non-printing character (NPC) is a code point (a number) in a character set, that does not represent a written symbol. They are used as in-band signaling to cause effects other than the ...

s, leaving 96

printable characters ASCII ( ), abbreviated from American Standard Code for Information Interchange, is a character encoding standard for electronic communication. ASCII codes represent text in computers, telecommunications equipment, and other devices. Because of ...

. This set of 96 printable characters includes upper and lower case letters, numbers, and basic math and punctuation. ASCII does not have enough room to include other common characters such as multi-national currency symbols or the various accented letters common in European languages. This led to a number of country-specific varieties of 7-bit ASCII with certain characters replaced. For instance, the UK standard simply replaced ASCII's hash mark, #, with the pound symbol, £. This normally led to different models of a given computer terminal or

printer Printer may refer to: Technology * Printer (publishing), a person or a company * Printer (computing), a hardware device * Optical printer for motion picture films People * Nariman Printer (fl. c. 1940), Indian journalist and activist * James ...

, differing only in the glyphs stored in ROM. Some of these were standardized as part of

ISO/IEC 646 ISO/IEC 646 is a set of International Organization for Standardization, ISO/International Electrotechnical Commission, IEC standards, described as ''Information technology — ISO 7-bit coded character set for information interchange' ...

. On an

8-bit clean ''8-bit clean'' is an attribute of computer systems, communication channels, and other devices and software, that handle 8-bit character encodings correctly. Such encoding include the ISO 8859 series and the UTF-8 encoding of Unicode. History ...

serial link, ASCII can be expanded to support a total of 256 characters. In this case, instead of replacing the characters in the original printable characters range from 32 to 127, new characters are added in the 128 to 255 range. This offers enough room for a single character set to include all the variety of characters used in North America and western Europe. This capability led to the introduction of the ISO/IEC 8859-1 standard character set containing 191 characters of what it calls the "Latin alphabet no. 1", but normally referred to as "ISO Latin".

Windows-1252 Windows-1252 or CP-1252 ( code page 1252) is a single-byte character encoding of the Latin alphabet, used by default in the legacy components of Microsoft Windows for English and many European languages including Spanish, French, and German. I ...

is a slightly expanded superset of ISO Latin. NRCS was introduced to solve the problem of requiring different terminals for each country by allowing characters in the basic 7-bit ASCII set to be re-defined by copying the glyph from the DEC's version of ISO Latin, the

Multinational Character Set The Multinational Character Set (DMCS or MCS) is a character encoding created in 1983 by Digital Equipment Corporation (DEC) for use in the popular VT220 terminal. It was an 8-bit extension of ASCII that added accented characters, currency symbols ...

(MCS). This meant that the ROM had to store only two character sets, standard ASCII and MCS, and could build any required local ASCII variant on the fly. For instance, instead of having a separate "UK ASCII" version of the terminal with a modified glyph in ROM, the terminal included an NRCS with instructions to replace the hash mark glyph with the pound. When used in the UK, typing Shift 3 produced the pound, the same keys pressed on a US terminal produced hash. The NRCS could be set through a setup command, or more commonly, by replacing the keyboard with a model that sent back a code when first booted. That way simply plugging in a UK keyboard, which had a pound sign on the 3 key, automatically set the NRCS to that same replacement.

NRC Sets

DEC terminals from the VT220 on had 12 different NRCS sets in addition to standard ASCII:

Notes

References

{{character encoding Character sets Digital Equipment Corporation

Description

NRC Sets

See also

Notes

References