Path: utzoo!attcan!uunet!mcvax!kth!enea!maxim!prc
From: prc@maxim.ERBE.SE (Robert Claeson)
Newsgroups: comp.windows.x
Subject: Re: 8 bits per char
Message-ID: <520@maxim.ERBE.SE>
Date: 3 Mar 89 19:12:29 GMT
References: <8902211720.AA14715@internal.apple.com> <722@acorn.co.uk> <727@acorn.co.uk>
Organization: ERBE DATA AB
Lines: 46

In article <727@acorn.co.uk>, john@acorn.co.uk (John Bowler) writes:

> This raises the question of what VT102 really does support, does anyone
> know whether:-
> 
> 1) It is capable of dealing with 8 bit received codes, as well as 7 bit.

No. It  can only handle various 7 bit character sets (ASCII is  only one
of them).

> 2) Whether there are mechanisms (like the compose character VT220 functionality)
>  to output 8 bit characters (or 7 bit representations of these)?

Nope.

> More investigation of xterm shows that both Alan Mimms and myself were
> half correct.  In fact xterm does not strip the parity bit on output (as
> Alan stated) but it does strip it on receipt of a character!

(Short code example deleted)

> so, you can type top-bit-set characters, and they get to the application,
> but they do not reflect as top-bit-set...   This must be a bug.

Yes, this is indeed a bug. A VT102 terminal can't handle 8 bit character
sets, but it sure can handle many different 7-bit character sets. The
old VT102 that's collecting dust at work uses one of the ISO 646 (I think)
codesets.

The point is, a VT102 emulator should be able to map the different 8859/1
codes into various 646 codes (user-selectable via a setup menu) and map
them back  again on output. In the swedish code set, the character at
the same position as the left bracket in the ASCII  character set is
A diareshis. The brackets and braces aren't there. Thus, when operating
in Swedish mode, braces should be ignored and  A diareshis should be
mapped into the right 7-bit position on input and output.

But really, it doesn't even need to perform the mapping. Just checking
what characters are legal in the  national character set and ignoring
the rest, and using 8859/1 internally, would be sufficient.

-- 
Robert Claeson, ERBE DATA AB, P.O. Box 77, S-175 22 Jarfalla, Sweden
Tel: +46 (0)758-202 50  Fax: +46 (0)758-197 20
EUnet:   rclaeson@ERBE.SE               uucp:   {uunet,enea}!erbe.se!rclaeson
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