Path: utzoo!utgpu!water!watmath!clyde!att!osu-cis!tut.cis.ohio-state.edu!ukma!psuvm.bitnet!cunyvm!ndsuvm1.bitnet!nu013809
From: NU013809@NDSUVM1.BITNET (Greg Wettstein)
Newsgroups: comp.dcom.modems
Subject: Re: Problems with MNP on a MultiTech 224EH
Message-ID: <1211NU013809@NDSUVM1>
Date: 26 May 88 13:57:50 GMT
References: <221@aoa.UUCP> <2315@ritcsh.UUCP>
Organization: North Dakota Higher Education Computer Network, Fargo, ND
Lines: 46
DISCLAIMER: Author bears full responsibility for contents of this article.

I have just received a Multitech MT-224EH modem and am setting it for
reliable (MNP Class 5/compressed mode) communications with another MT-224EH.
I have read the manual thoroughly and have wired an RS-232 cable which
supports all nine lines (SEND, RECEIVE, GND, RTS, CTS, RI, DSR, DTR, CD).
I have written my own terminal emulator (MSC C 5.0 + assembler) which
supports interrupt driven asynchronous communications.  I run the terminal
emulator on a Zenith Z-159 and use the MT-224EH to dial into an ITT
XTRA (with another MT-224EH) running SCO XENIX.

My desire is to run both modems at 4800 baud to take complete advantage
of the increased throughput provided by the MNP protocol as well as
data compression.  Since one of my desires is binary file transfers using
the IMODEM protocol my interpretation is that hardware handshaking using
CTS/RTS control pairs is the only feasible method of flow control.

The problem that I am having with CTS/RTS control pairs is with the initial
state of the control signals.  I have set the internal jumper so that
RTS is not forced high (functions normally) and have correctly set SWITCH 1
on the internal four pole switch so that CTS follows the RTS signal.  Even
though my terminal emulator raises RTS in its initialization procedure the
modem refuses to acknowledge with CTS and of course this hangs an emulator
using CTS/RTS control pairs.  It apprears that the Multitech modem will not
raise CTS (even in the presence of RTS) unless a valid carrier detect is
available.  I have a copy of QMODEM 3.1 and it also complains that CTS is
not available when it attempts to initialize the serial port.

My question is whether or not I have missed some control switch setting or
perhaps some internal jumper is still mis-configured.  The manual that
comes with the modem is pretty good but I do not think that the section
describing hardwire flow control does a good job of documenting exactly
what has to be done.  I am in the middle of a catch-22 because I cannot
initiate a call without a valid CTS and I cannot seem to get a valid CTS
until a valid connection is achieved.  The only thing I have been able
to think of is to write code into my terminal emulator which does not
attempt RTS/CTS flow control until a valid DSR signal is elicited by the
modem.

Any suggestions, comments or questions would be greatly appeciated.  I have
a pretty fair background in PC's and asynchronous communications so responses
at any level of expertise would be gratefully accepted.  I will summarize
all responses back to the net.  Thanks in advance to all respondents.


                                        As always,
                                        G.W. Wettstein
                                        NU013809@NDSUVM1