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From: root@zswamp.uucp (Geoffrey Welsh)
Newsgroups: comp.dcom.modems
Subject: "Null Terminal" Cable.
Message-ID: <106.2843277B@zswamp.uucp>
Date: 28 May 91 13:35:15 GMT
Organization: Izot's Swamp BBS (FidoNet), Kitchener, Ontario
Lines: 32


 >From: bwrdmond@vax1.tcd.ie

 >Is there such a beast as a "Null Terminal" cable - i.e. a 
 >DCE to DCE connection?

   Offhand, I'd say that you *might* be able to use a null modem cable to 
accomplish this, even though an ideal null terminal cable ("DCE bridge"?) 
might need to be wired differently.

 >If a modem will respond to RTS by raising CTS even while DTR 
 >is low then it seems fairly straightforward. Is this the case?

   Not with dialup async modems, which either leave CTS asserted and ignore 
RTS (dy default, anyway) or use them for hardware flow control.  In that 
case, one modem's CTS output would have to be wired to the other's RTS input; 
DSR (effectively 'modem ready') should be wired to the other modem's DTR 
(effectively 'modem enable') and (of course), the TxD and RxD should be 
crossed.  Sounds a bit like the null modem cables I use.

   I suppose that you should wire the thing such that DTR drops for about two 
seconds when carrier detect goes from true to false, but that makes this a 
device as much as a cable.

   These specs are by no means complete.
 

--  
Geoffrey Welsh - Operator, Izot's Swamp BBS (FidoNet 1:221/171)
root@zswamp.uucp or ..uunet!watmath!xenitec!zswamp!root
602-66 Mooregate Crescent, Kitchener, ON, N2M 5E6 Canada (519)741-9553
"He who claims to know everything can't possibly know much" -me