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From: russotto@eng.umd.edu (Matthew T. Russotto)
Newsgroups: comp.sys.apple2
Subject: Re: hardware handshaking through a modem
Summary: Behold! A technical post
Message-ID: <1990Oct6.210432.24572@eng.umd.edu>
Date: 6 Oct 90 21:04:32 GMT
References: <2092@unsvax.NEVADA.EDU>
Sender: news@eng.umd.edu (The News System)
Organization: College of Engineering, Maryversity of Uniland, College Park
Lines: 31

In article <2092@unsvax.NEVADA.EDU> alfter@uns-helios.nevada.edu (SCOTT ALFTER) writes:
>A feature I recently added was XON/XOFF handshaking.  When the buffer contains
>128 characters, the daemon automatically sends XOFF.  XON is sent to resume
>operation when the buffer's contents drop to 64 characters.
>
>XON/XOFF handshaking is fine for an interactive session, but what about file
>transfers?  You need all 256 possible byte values available for most file
>transfer protocols (some, such as Kermit, make do with less), so you can't use
>handshaking that adds stuff to the bitstream.  The obvious solution is hardware
>handshaking--playing with the DTR line.  However, this doesn't seem to work.  I
>reassembled my modem driver for DTR instead of XON/XOFF and called a BBS at
>2400 baud, using a BASIC program to interface with the ML routines.  With XON/
>XOFF, incoming text was whole--it appeared slowly, but you'd get it all.  With
>DTR, though, large chunks of text would be missing.  All I'm doing is playing
>with bit 0 of the ACIA's command register--a 1 means ready, 0 should tell the
>remote device not to send.  My Imagewriter works this way; are modems
>different?  Do handshaking signals get sent, or is XON/XOFF the only
>possibility?

DTR low means 'drop carrier' to modems, or means nothing, depending on the
setting of various DIP switches.  You want to use CTS/RTS, not DTR.
(CTS and RTS are on pins 4 and 5, DTR is on pin 20.  There may be jumpers
on the Super Serial to enable/disable these-- there are on my CCS 7711, based
on the same chip)

Your other alternative is to wire Pin 20 (DTR) of the Super Serial Card to
pin 4 (RTS) of the modem.  It's probably better to change your program to
use RTS, though.
--
Matthew T. Russotto	russotto@eng.umd.edu	russotto@wam.umd.edu
      .sig under construction, like the rest of this campus.