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From: RAF@CU.NIH.GOV ("Roger Fajman")
Newsgroups: comp.dcom.modems
Subject: Clarification on MNP4 and Everex 24+
Message-ID: <9102181939.AA12524@alw.nih.gov>
Date: 18 Feb 91 19:38:41 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
Lines: 20

> Alas, there's nothing I can do about other people's modems but
> advise users to contact the manufacturers are suggest an S-register
> to control the flow-off threshold.  I guess this is one more
> argument in favor of using Hayes modems, since we've kept the
> buffers small (256 bytes, with 192-byte high water mark) all along.

The USR Courier 9600 bps modems have an S-register setting for this.
Setting S15=8 reduces the buffer to 128 bytes (instead of 1.5K) for
non-ARQ mode.  The stated reason for the large buffer is the ability to
do XMODEM and YMODEM file transfers without flow control (presumably
with the RS-232 interface locked at high speed on a low speed call).
Why one would lock the interface at high speed without flow control is
not so clear to me.  I suppose that one might want to do it on a
machine that does not support hardware flow control, but then it seems
like a larger buffer might be desirable.  Perhaps 1.5K is big enough to
hold most screenfuls of text encountered in practice.

Roger Fajman                                   Telephone:  +1 301 402 1246
National Institutes of Health                  BITNET:     RAF@NIHCU
Bethesda, Maryland, USA                        Internet:   RAF@CU.NIH.GOV