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From: jimb@amdcad.UUCP (Jim Budler)
Newsgroups: net.micro.mac
Subject: Re: DTR held high from program control?
Message-ID: <12993@amdcad.UUCP>
Date: Fri, 12-Sep-86 14:02:58 EDT
Article-I.D.: amdcad.12993
Posted: Fri Sep 12 14:02:58 1986
Date-Received: Fri, 12-Sep-86 22:26:00 EDT
References: <458@aecom.UUCP> <3773@nsc.UUCP>
Reply-To: jimb@amdcad.UUCP (Jim Budler)
Distribution: net
Organization: AMD, Sunnyvale, California
Lines: 32

In article <3773@nsc.UUCP> curry@nsc.UUCP (Ray Curry) writes:
+---------------
| 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.
+---------------

Ah Ha, so that explains it. I've been hearing all this talk about MacTerminal
cycling DTR with the new ROMS, and it never happens to me. Well I
have the New ROMS, in an upgraded 512. I suspect that the Mac+ has been
redesigned slightly to use the DTR. 

If you have the new ROMS, you may be able to rewire it as described and
have it work, since the New ROMS do cycle the DTR (per IM vol IV).


-- 
 Jim Budler
 Advanced Micro Devices, Inc.
 (408) 749-5806
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I got tired of my old signature.