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From: jc@minya (John Chambers)
Newsgroups: comp.unix.wizards
Subject: DTR response time?
Message-ID: <350@minya.UUCP>
Date: Sat, 31-Oct-87 23:18:02 EST
Article-I.D.: minya.350
Posted: Sat Oct 31 23:18:02 1987
Date-Received: Thu, 5-Nov-87 06:34:13 EST
Sender: std@minya.UUCP
Lines: 32

Well, I got so many responses to my last question, that I thought I'd
try to stump y'all with another.  You know the CTS/DTR protocol that
a lot of terminals use?  Sure, you do.  When the device (terminal or
printer or whatever) finds that its buffer is full, it changes the 
value of pin 20 on the RS-232 connector.  The computer's serial card
interprets this to mean that the device is incapacitated, and stops
sending characters.  Later, when the poor device has caught up, it
flips pin 20 (aka DTR or Data Terminal Ready or something like that),
the computer notices that the device is back, and starts transmitting.

It seems that many computers, including this one, don't stop instantly
when DTR drops; they transmit up to N more characters before stopping.
Some time ago, I saw a machine that would send 128 more bytes before
stopping.  You can imagine how well this worked for some devices with 
small buffers.

This machine is nicer; it only transmits about 8 bytes after DTR has
dropped.  This seems OK for most purposes, but I seem to have a printer
that can't even handle that.  I suspect that, when it drops DTR, it
sometimes can't handle even one more character.  (Presumably it will
accept the current one.)  

Anyhow, the puzzle is this:  Is there a way to control this behavior
of the driver and/or serial board in a reasonably generic Sys/V?  Can
I set the above value of N?  I seem to remember some vague rumor that
this can be done somehow, but I just can't find anything about it in
the kwic index.  Neither can grep.  Maybe I just don't know the right
words to look up.  Maybe it isn't documented.  Maybe I can't get there
from here.  

I'd love a "RTFM" response, if it comes accompanied by a section and
page number (or even telling me how it's kwic-indexed).