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From: jb10320@uxa.cso.uiuc.edu (Desdinova)
Newsgroups: comp.sys.apple2
Subject: Re: hardware handshaking through a modem
Message-ID: <1990Oct6.181920.3936@ux1.cso.uiuc.edu>
Date: 6 Oct 90 18:19:20 GMT
References: <2092@unsvax.NEVADA.EDU>
Sender: news@ux1.cso.uiuc.edu (News)
Organization: University of Illinois at Urbana
Lines: 41

In article <2092@unsvax.NEVADA.EDU> alfter@uns-helios.nevada.edu (SCOTT ALFTER) writes:
[about his term program]
>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?
    a 0 does tell the remote device not to send.  Unfortunately, the remote
device is YOUR modem.  DTR only controls the computer-modem connection.
Most modems allow a DTR drop to hang up the modem (that's how ZLink and TelCom
do it).
    There's no way around XON/XOFF- it's the only method of over-the-phone
handshaking.  You can usually pick whichever characters XON and XOFF are,
with Kermit and Zmodem. With XModem and YModem, handshaking is not a problem,
since just about any computer can handle a 1K burst (with a small buffer).
ZModem is where the problem begins to happen on an apple II (disk access
kills ACIA/SCC interrupts, making Zmodem freak).
    You must have your XON/XOFF handshaking turned off during a transfer.
It's the only way.  

>Thanx in advance for any help with this problem.
>Scott Alfter                             _/_
>                                        / v \ Apple II:
>Internet: alfter@uns-helios.nevada.edu (    ( the power to be your best!
>   GEnie: S.ALFTER                      \_^_/


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                            |                             (B O'Cult)
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