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Path: utzoo!linus!philabs!cmcl2!seismo!rlgvax!guy
From: guy@rlgvax.UUCP (Guy Harris)
Newsgroups: net.unix-wizards
Subject: Re: laser printers and 8 bit serial
Message-ID: <580@rlgvax.UUCP>
Date: Sat, 16-Mar-85 12:38:33 EST
Article-I.D.: rlgvax.580
Posted: Sat Mar 16 12:38:33 1985
Date-Received: Sun, 17-Mar-85 23:10:57 EST
References: <6500002@hp-sdd.UUCP> <84@mit-athena.UUCP> <4256@ucla-cs.ARPA>
Organization: CCI Office Systems Group, Reston, VA
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> It seems to me that RAW mode and TANDEM mode are not necessarily orthogonal
> if you take RAW to mean that no characters have special meaning. (They
> aren't cooked.) In TANDEM mode ^S and ^Q are special. How do you pass
> a ^S when in RAW and TANDEM mode at the same time? (Such as emacs might want)
> I believe this is the case in the 4.1bsd tty driver, perhaps System 5
> is different.

1) As Chris's article points out, RAW doesn't affect TANDEM at all.  TANDEM
doesn't affect what happens when the computer *receives* ^S or ^Q.  It
merely conditions the computer to *send* ^S when its buffers are getting
too full, and ^Q when they become sufficiently empty.

2) Why would EMACS want TANDEM mode?  EMACS wants an 8-bit data path on
terminals which have a META key which turns the 8th bit on, and may want
to disable special processing of ^S and ^Q on *input* (because people
tend to bind ^S to "search" and ^Q to "quote" - VT100s in smooth-scroll
mode *require* ^S/^Q flow control, and some versions of EMACS bind different
keys to "search" and "quote", and leave ^S/^Q processing on, to enable this).
The only way to do that in V7, or 4.xBSD, is to turn on RAW mode.  In
Systems III and V, the 8-bit data path can be selected by changing the
character size to 8 bits, disabling parity, and disabling stripping of
characters to 7 bits.  The handling of ^S/^Q on input can be disabled by
turning off the IXON mode.

If you're in RAW and TANDEM mode at the same time, any ^S or ^Q *received*
by the computer goes straight to the application program.  However, the
computer *will* send ^S and ^Q for flow control.
-- 
	Guy Harris
	{seismo,ihnp4,allegra}!rlgvax!guy