A normal RS-232 connection is made between one DTE device and one DCE device. To connect DTE-to-DTE or DCE-to-DCE, you need a special cable or adapter known as a "Null Modem". ////////////////////////////////////////////////////////////////////////////// Newsgroups: comp.terminals Organization: http://extra.newsguy.com References: <3D18E386.95FF66@yahoo.com> Message-ID: <3D269BCD.2000805@valid.net> Date: Sat, 06 Jul 2002 02:27:09 -0500 From: Andy Ball Subject: Re: Null modem cable wiring This is a wiring scheme Terminal Computer that has worked well for me in the past. DB25 DB9 1 FG (see notes) A lot depends on the equipment that you are 2 TXD -------\/------- TXD 3 connecting together, and 3 RXD <------/\------> RXD 2 there is really no substitute for a decent 4 RTS -------\/------- RTS 7 manual (sadly a rare thing 5 CTS <------/\------> CTS 8 these days). 20 DTR -------\/------- DTR 4 For instance, I read the 6 DSR <--+---/\---+--> DSR 6 other day that the Wyse 55 8 DCD <--' `--> DCD 1 terminals do not implement the RTS and CTS lines 7 SG ---------------- SG 5 commonly used for hardware flow control. Use screened cable and connect the screen to pin 1 at the terminal end only (this is the 'Frame Ground' pin). At either end you may not need to connect DCD (data carrier detect). It depends on whether the terminal or the software running on the host computer demand it. The gender of the connectors usually has no bearing on their wiring. I think at one time the convention was to use female connectors on equipment and male on cables (since equipment had power applied, female connectors were less easily shorted and are probably more robust than male ones). IBM chose to use male connectors on the PC's serial ports, perhaps to differentiate them from their DB25 female parallel port). I hope the above diagram is clear enough, and that you find it useful. - Andy. ////////////////////////////////////////////////////////////////////////////// From gjohnson@dream.season.com Mon Oct 28 09:59:58 1996 Path: stc06.ctd.ornl.gov!fnnews.fnal.gov!lll-winken.llnl.gov!enews.sgi.com!www.nntp.primenet.com!nntp.primenet.com!howland.erols.net!news.mathworks.com!uunet!in2.uu.net!fox.almaden.ibm.com!garlic.com!news.scruz.net!gjohnson From: gjohnson@dream.season.com (Reality is a point of view) Newsgroups: comp.terminals Subject: Pick a number of wires, almost any number . . . Date: 23 Oct 1996 22:13:28 GMT Organization: season.com [205.179.33.0] Lines: 145 Message-ID: NNTP-Posting-Host: 205.179.33.42 During my search for the best thing to do with six wires I helped someone that only had three and got the following response, which might be interesting to readers here. -- Gary Johnson "Rosebud . . ." gjohnson@season.com Freedom? CAMPAIGN '96: Juck 'em if they can't fake a toke. From: Francesco Potorti` Newsgroups: comp.os.linux.networking Subject: Re: TCP/IP over null modem? Message-ID: gjohnson@dream.season.com (Reality is a point of view) writes: I wish I knew which connections were best when there are six wires available. I have this note. I copied it from various sources. The only one I really tried is the last one, to be used while connectin two PCs with the DOS program whose name I can't remember (standard with msdos > 5.0) 7 wires null modem connections for V24 protocol on RS-232 DTE DTE 2 [>]------\ /------[<] 2 TX [ ] \ [ ] 3 [<]------/ \------[>] 3 RX [ ] [ ] 4 [>]-\ /-[<] 4 RTS [ ] | | [ ] 5 [<]-+---\ /---+-[>] 5 CTS [ ] \ / [ ] 6 [<]----\ / /----[>] 6 DSR [ ] \/ \/ [ ] 7 [-]-----/\-/\-----[-] 7 GND [ ] / \ \ [ ] 8 [<]---/ / \ \---[>] 8 DCD [ ] / \ [ ] 20 [>]----/ \----[<] 20 DTR 3 wires null modem connections for V24 protocol on RS-232 DTE DTE 2 [>]------\ /------[<] 2 TX [ ] \ [ ] 3 [<]------/ \------[>] 3 RX [ ] [ ] 4 [>]-\ /-[<] 4 RTS [ ] | | [ ] 5 [<]-/ \-[>] 5 CTS [ ] [ ] 6 [<]-\ /-[>] 6 DSR [ ] | | [ ] 7 [-]-|-----------|-[-] 7 GND [ ] | | [ ] 8 [<]-+ +-[>] 8 DCD [ ] | | [ ] 20 [>]-/ \-[<] 20 DTR Null modem on the MISCO catalogue (DTE) DTE DTE 1 [-]---------------[-] 1 GND [ ] [ ] 2 [>]------\ /------[<] 2 TX [ ] \ [ ] 3 [<]------/ \------[>] 3 RX [ ] [ ] 5 [<]-\ /-[>] 5 CTS [ ] | | [ ] 6 [<]-\ /-[>] 6 DSR [ ] | | [ ] 7 [-]-|-----------|-[-] 7 GND [ ] | | [ ] 8 [<]-+----\ /----+-[>] 8 DCD [ ] \ [ ] 20 [>]------/ \----\-[<] 20 DTR Null modem on the MISCO catalogue (DCE) DCE DCE 1 [-]---------------[-] 1 GND [ ] [ ] 2 [>]------\ /------[<] 2 TX [ ] \ [ ] 3 [<]------/ \------[>] 3 RX [ ] [ ] 4 [>]-----\ /-----[<] 4 RTS [ ] \ / [ ] 5 [<]----\ \ /----[>] 5 CTS [ ] \/ \/ [ ] 6 [<]-----/\ /\-----[>] 6 DSR [ ] \ [ ] 7 [-]------/-\------[-] 7 GND [ ] / \ [ ] 20 [>]----/ \----[<] 20 DTR Null modem for PC DCE DCE 2 [>]------\ /------[<] 2 TX [ ] \ [ ] 3 [<]------/ \------[>] 3 RX [ ] [ ] 4 [>]------\ /------[<] 4 RTS [ ] \ [ ] 5 [<]------/ \------[>] 5 CTS [ ] [ ] 6 [<]-----\ /-----[>] 6 DSR [ ] \ / [ ] 7 [-]-------\-------[-] 7 GND [ ] / \ [ ] 20 [>]-----/ \-----[<] 20 DTR -- Francesco Potorti` Voice: +39-50-593203 Computer Network Group Operator: +39-50-593211 CNUCE-CNR, Via Santa Maria 36 Fax: +39-50-904052(G3)/904051(G4) 56126 Pisa - Italy Email: F.Potorti@cnuce.cnr.it //////////////////////////////////////////////////////////////////////////////