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From: lasko@regina.DEC (Video Terminals Architecture)
Newsgroups: net.info-terms,net.std
Subject: Re: information about National Replacment Character sets
Message-ID: <3284@decwrl.UUCP>
Date: Thu, 25-Jul-85 11:21:53 EDT
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Posted: Thu Jul 25 11:21:53 1985
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>Is there any standard that describes what DEC calls National Replacement
>Character Sets (NRC sets)?  
>	Ed Jennings                    

A National Replacement Character set is a set of 94 graphic characters
(encoded in a 7-bit code) produced by replacing certain characters
in the ISO standard International Reference Version (IRV) character set.

The IRV set and the permissible variations are described in ISO 646.
ASCII, as Martin Minow mentioned in an earlier posting, is only a variation 
on the IRV set: ASCII places the dollar sign ($) where the IRV set places 
the General Currency symbol (looks like an o superimposed on an x).  

The permissible variations of the IRV set are the possible replacement
of "#" (number sign, position 2/3 in the code table) by the (British) Pound 
sign, the General Currency sign by "$" (dollar sign, position 2/4), and 
substitutions for these ten characters:  "@" (commercial at sign, 4/0), "[" 
(left square bracket, 5/11), "\" (backslash, 5/12), "]" (right square bracket,
5/13), "^" (circumflex, 5/14), "`" (grave accent, 6/0), "{" (left curly
bracket/brace, 7/11), "|" (vertical bar, 7/12), "}" (right curly bracket/brace,
7/13), and "~" (tilde/overline 7/14).  

ECMA, the European Computer Manufacturers Association, as designated by ISO
maintains the "International Register of Coded Character Sets to be used 
with Escape Sequences", wherein ISO standard NRC sets are registered, in 
accordance with the rules of ISO 2375 "Data Processing - Procedures for 
the Registration of Escape Sequences".  

The register also contains several sets which are not variations of the
IRV, of course, such as Katakana, Greek, Cyrillic, and Videotex sets.
As Martin mentioned, in general, NRC sets are standardized by national
standards organizations, however, individual companies may register sets,
when sponsored by a standards body.

The registration also consists of the assignment of intermediate and final 
characters which are a part of the escape sequence used to select that 
particular character set. The escape sequence used to select the character 
set is described in ISO 2022, "Code Extension Techiques for use with the 
7-bit Coded Character Set" (of ISO 646).  

(ISO 6429 is "Additional Control Functions for Character-Imaging Devices" 
and contains lots of different types of device control functions, [e.g. 
positioning, editing, rendition, etc.], but only marginally touches on 
specific character sets.)
 
Tim Lasko
Digital Equipment Corporation  Maynard, Mass.
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