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From: jeffn@nuchat.UUCP (Jeff Noxon)
Newsgroups: comp.sys.apple2
Subject: Re: hardware handshaking through a modem
Message-ID: <29113@nuchat.UUCP>
Date: 7 Oct 90 13:46:42 GMT
References: <2092@unsvax.NEVADA.EDU> <1990Oct6.122802.28306@nntp-server.caltech.edu>
Reply-To: jeffn@nuchat.UUCP (Jeff Noxon)
Organization: Houston Public Access
Lines: 39

In article <1990Oct6.122802.28306@nntp-server.caltech.edu> toddpw@tybalt.caltech.edu (Todd P. Whitesel) writes:
|When you use the hardware handshake lines, you are telling the modem that
|it is ok/not ok to send, but the modem has no way to communicate this fact
|to the other end of the phone line. This means that your modem will quit
|sending characters, but the modem itself will still be recieving them --
|so when the modem's own internal buffer (assuming it has one) overflows,
|you lose gobs of characters.
|
|My suggestion would be to have your drivers be able to turn XON/XOFF mode
|on or off, so the higher-ups can inform the driver whether or not to use
|XON/XOFF. A bigger buffer than 256 characters would also be a good idea if
|you are not really tight on memory.
|
|Todd Whitesel
|toddpw @ tybalt.caltech.edu

Is hardware handshaking even supported by any of the GS term programs?  But
anyway, the only reason I can see anyone wanting to do this is if they have
a high speed or MNP modem.  Take this example:  My T2500, in PEP mode, runs
on the average at about 17kbps.  The DTE rate (Modem<->Computer) is set to
19.2kbps.  This makes it easy to overrun the modem's buffer and lose
characters.  Handshaking prevents this from happening.  It works in two ways:
the modem tells you when it's buffer is full, and you tell the modem when
your buffer is full.

Every high speed protocol I have heard of communicates this information with
the other modem as well.  It's built in with PEP.  Other modems use MNP and
V.42 to take care of this.

If your XON/XOFF handshaking is acknowleged by the modem as handshaking,
you're in trouble because file transfers will fail.  That's why the hardware
solution is best, if possible.

Jeff

-- 
Jeff Noxon                      | Stop complaining and do something about
jeffn@nuchat.sccsi.com          | it.  Really!
713/721-6820 (CDT) Houston, TX  |