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From: merlyn@avalon.UUCP (Steve Humphrey)
Newsgroups: net.micro.att
Subject: Re: Hayes modem and the 3b2
Message-ID: <103@avalon.UUCP>
Date: Thu, 30-May-85 11:44:20 EDT
Article-I.D.: avalon.103
Posted: Thu May 30 11:44:20 1985
Date-Received: Fri, 31-May-85 04:15:18 EDT
References: <101@gwsd.UUCP>
Organization: AT&T-Information Systems, Lincroft, NJ
Lines: 52

> There is a problem using the Hayes modems as an ACU.
> 
> To originate calls (outgoing) you must disable the carrier detect (switch 6).
> To receive calls (incoming) you must enable carrier detect.
> 
> Has anyone figured out a way to allow you to use a Hayes modem on a uucp
> bi-directional line?
> 
> Bob

No, it is not possible with the standard software to use the Hayes
modem bidirectional. Reason: The cu/uucp software accesses a modem
in a way that requires DCD to be up. The 3B2 is capable of allowing
access with DCD down, and I've modified the cu/uucp software to do
that. Even running that modified software, though, I still had
minor problems with the modem, thus I don't use it any more. (I never
identified the problems, so I don't know who to blame.)

I sent my software modification to DAN (as in Honey-DanBer UUCP)
so it may appear in a later release.

If you find it expensive to (1) toss out a pile of Hayes modems
and buy other modems (e.g. Ventel, Penril, AT&T 2224C all work fine),
(2) use two ports on the 3B2 (one incoming, one outgoing), or
(3) buy the source so you can do the software fix, then consider
a hardware work-around:

The Hayes keeps the CTS (Clear To Send) signal up while connected
to the 3B2. The work-around is to build a small circuit that uses
CTS and DCD from the modem to build a pseudo-DCD signal for the
3B2. The trick is to keep the pseudo-DCD signal up while the CTS
signal is up, regardless of the state of the DCD signal, EXCEPT
when the DCD goes from high to low (i.e. when a connection to a
remote machine is dropped). At that transition, the circuit drops
the pseudo-DCD for a short interval (about one second should be
enough) then raises it again. This tells the cu/uucp software
that the connection dropped, so the software quits; raising the
pseudo-DCD back up again lets another outgoing call be placed.

What does the circuit look like? I wish I knew, sorry. We were
starting to design the circuit, since we have a closet full of
Hayes modems that we'd like to use, but other work took
precedence. Interested parties can drop me a note and I'll
give you what info I have, but be warned: I'm not a hardware jock
so I don't know much more than I've described above.

			Steve Humphrey
			...!avalon!merlyn
			AT&T
-- 
			Steve Humphrey
			hogpc!merlyn or lz3f310!merlyn