Xref: utzoo comp.dcom.modems:4602 sci.electronics:8061
Path: utzoo!attcan!uunet!opel!johnk
From: johnk@opel.uu.net (John Kennedy)
Newsgroups: comp.dcom.modems,sci.electronics
Subject: Anyone have a modem dialing out on two lines?
Message-ID: <282@opel.uu.net>
Date: 1 Oct 89 22:18:57 GMT
Reply-To: johnk@opel.UUCP (John Kennedy)
Organization: Second Source, Inc., Annapolis, MD
Lines: 41

Got a Telebit Trailblazer+, and two phone lines serving two dialing
areas.  I'm trying to come up with a scheme that allows me to
dial out on either of the two lines.

I'm assuming that I'll use some sort of solid state relay, or
even a telephone crosspoint chip, but don't know yet how I'll
control it.

So far, the options I'm considering are:

1)  A device driver in the host system that will toggle a lead.
    This would be actuated just prior to sending the dialing
    sequence to the modem, and reset at the end of the call.

2)  A UART and controller which listens to the AT sequence being
    sent to the modem, and which switches lines upon detection
    of a certain AT sequence.

3)  A DTMF decoder which listens to an outpulsed sequence from the modem,
    then connects one of the two lines in time for the delayed, real
    digits.

4)  If I replaced the modem with a Telebit T2000, the option exists
    to assert the A/A1 leads (second pair) coming out of the modem.
    Techs at Telebit confirmed that the TB+ does not have this capability.
    These leads could be used to control the switching.  Anyone
    using these?

Option 1 would require the least hardware, but I have a concern about
leaving the wrong line connected in case of an aborted dialing attempt.

Anyone done anything similar, or have any suggestions?

Thanks in advance,

John

-- 
John Kennedy                     johnk@opel.uu.uunet
Second Source, Inc.
Annapolis, MD