Article 3341 of rec.ham-radio.packet: Path: n8emr!tut.cis.ohio-state.edu!pacific.mps.ohio-state.edu!zaphod.mps.ohio-state.edu!rpi!batcomputer!payne From: payne@batcomputer.tn.cornell.edu (Andrew Payne) Newsgroups: rec.ham-radio.packet Subject: Re: Daisy-chained RS-232 cable Keywords: RS-232, NET, NET-ROM. Message-ID: <10098@batcomputer.tn.cornell.edu> Date: 12 Apr 90 14:59:43 GMT References: <122@bongo.UUCP> Reply-To: payne@tcgould.tn.cornell.edu (Andrew Payne) Organization: Cornell Theory Center, Cornell University, Ithaca NY Lines: 139 In article <122@bongo.UUCP> julian@bongo.UUCP (Julian Macassey) writes: > > I would like to join the serial ports of several computers together >so I can run KA9Qs SLIP between then. Sort of poor man's Ethernet. I >know that a similar trick is used to join several TNCs together for >multi NET-ROM use. The trick involves resistors and diodes I believe. > > Does anyone have details on how to daisy-chain RS-232 ports? > I've got some docs here on hooking Net/Rom nodes back to back. It lists a product called a ".. TJP Octopus which is a diode matrix board that allows up to 8 TNCs to be tied together with minimum hassle. The board is available from John Painter 7 Jefferson Street Nashua, NY 03060 for $15. Information on the board may be gotten for a S.A.S.E at the same address." I have neither used nor seen the card. Digging through the TheNET DOCUMENTATION, I found the following diagrams which may be of use: ***** Start of excerpt ***** -------------------------------------------------------------------------- Connector Cable for 2 TNCs Interlink Operation TNC 1 TNC 2 signal +----+ +----+ I 1 I---------------------------------------I 1 I prot. ground I I I I I 2 I-------------. .--------------------I 2 I Tx data I I .----+----. I I I 3 I------------------. .---------------I 3 I Rx data I I I I I 5 I--- ---I 5 I CTS I I I I I 20 I--- ---I 20 I DTR I I I I I 7 I---------------------------------------I 7 I signal ground I I I I I 10 I---. .---I 10 I V- I I I I I I I 23 I---. .---I 23 I DRS I I I I +----+ +----+ -------------------------------------------------------------------------- Connector Cable for 3 TNCs Interlink Operation TNC 1 +----+ I I I 1 I--------. I I I I 2 I--------+---------------------------------------------------X----. I I I I I I 3 I--------+----------------------------------------X------. I I I I I I I K K I 5 I--------+-----------X--------------. I I A A I I I I I I I I I I 20 I--------+-----------+--------------+-----X---. I I I I I I I I I I I I I I I I 7 I--------+---. I I I I I I I I I I I I I I A A I I I I I 10 I---. I I I I K K I I I I I I I I I I I I I I I I I I 23 I---. I I I I I I I I I I I I I I I I I I I I I I +----+ I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I TNC 2 I I I I I I I A I I +----+ I I I I I I I K I I I I I I I I I I I I I I I 1 I--------X I I I I I I I I I I I I I I I I I I I I I I 2 I--------+---+-------+--------------+-----+---+---+------X I I I I I I I I I I I I I I I 3 I--------+---+-------+--------------+-----+---+---+--X---+---. I I I I I I I I I I I I I I 5 I--------+---+--X----+--------------+-----. I I I I I I I I I I I I I A A I I I 20 I--------+---+--+----+--------------X----. I K K K I I I I I I I I I I I A I I 7 I--------I---X I I I I I I I I I I I I I I I I I I I I I 10 I---. I I I I I I I I I I I I I I I I I A I I I I I I 23 I---. I I I K K I I I I I I I I I I A I I I I I I +----+ I I K I I I I I I I I I A I I I I I I I I I I I I I I I I I TNC 3 I I I I I I I I I I +----+ I I I I I I I I I I I I I I I I I I I I I I I 1 I--------. I I I I I I I I I I I I I I I I I I I I I 2 I------------+--+----+-------------------+----+---X--. I I I I I I I I I I I I 3 I------------+--+----+-------------------+----+----------X--------. I I I I I I I I 5 I------------+--+----+-------------------X---.I I I I I I I 20 I------------+--X----. I I I I 7 I------------. I I I 10 I---. X = connection I I I + = cross over I 23 I---. A = anode of a 4148 diode I I K = cathode of a 4148 diode +----+ ***** End of excerpt Looking at the diagram for the 3-node interconnect I notice that they are using CTS and DTR (pins 5 & 20). From the way they are interconnected, I'd guess that these lines are used for a activity indicator, much in the same way the Carrier Detect is used on the air. I do not know if the SLIP code does this as well, so you may be at the mercy of probability: a node has no way to check if the serial line is already in use before transmitting. Comments? -- = = = = = = = = = = = = = = = = = = = = = = = = = = = Andrew C. Payne, N8KEI UUCP: ...!cornell!batcomputer!payne INTERNET: payne@tcgould.tn.cornell.edu