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From: curry@nsc.UUCP (Ray Curry)
Newsgroups: net.micro.mac
Subject: Re: DTR held high from program control?
Message-ID: <3773@nsc.UUCP>
Date: Fri, 12-Sep-86 00:36:09 EDT
Article-I.D.: nsc.3773
Posted: Fri Sep 12 00:36:09 1986
Date-Received: Fri, 12-Sep-86 05:11:42 EDT
References: <458@aecom.UUCP>
Reply-To: curry@nsc.UUCP (Ray Curry)
Distribution: net
Organization: National Semiconductor, Sunnyvale
Lines: 11

According to schematics I have for the 512 Mac, the dtr pin on the scc is
not connected at all.  The pin 6 of the connector is permanently tied to
+12 volts.  I hear Apple had trouble hooking in their telephone system 
with built in modems because dtr was permanently held high.  
Perhaps newer macs have changed this but I have never had my modem hang
up even when exiting macterminal and returning.  I have been tempted to
try opening the mac and connecting the dtr up, but since the scc has to
be initialized to use the dtr pin, it would impact any software not doing
so, so I haven't.  Has anybody every confirmed with a breakout box that
the dtr signal ever moves?  Perhaps rts/cts are being used and refered to
as dtr.