X-Andrew-WideReply: netnews.comp.sys.amiga.datacomm X-Andrew-Authenticated-as: 0;andrew.cmu.edu;Network-Mail Received: via nntpserv with nntp; Fri, 12 Nov 1993 12:59:07 -0500 (EST) Path: andrew.cmu.edu!bb3.andrew.cmu.edu!news.sei.cmu.edu!cis.ohio-state.edu!magnus.acs.ohio-state.edu!math.ohio-state.edu!sdd.hp.com!decwrl!pa.dec.com!zowie.zso.dec.com!ridder From: ridder@zowie.zso.dec.com (Hans) Newsgroups: comp.sys.amiga.datacomm Subject: Re: Null-modem cable Date: 12 Nov 1993 17:33:32 GMT Organization: Digital Equipment Corporation - DECwest Engineering Lines: 49 Message-ID: <2c0hdc$r4a@usenet.pa.dec.com> References: <2b3c1s$8no@delphinium.rtsg.mot.com> <1993Nov12.043555.22556@usage.csd.unsw.OZ.AU> NNTP-Posting-Host: zowie.zso.dec.com In article <1993Nov12.043555.22556@usage.csd.unsw.OZ.AU> s8437378@cse.unsw.edu.au (Andrew Kemmis Smith) writes: >In article <2b3c1s$8no@delphinium.rtsg.mot.com> king@rtsg.mot.com writes: >> >> TXD ( 2) ---------\ /--------- TXD ( 2) Transmit Data (output) >> X >> RXD ( 3) ---------/ \--------- RXD ( 3) Received Data (input) >> >> RTS ( 4) ---------\ /--------- RTS ( 4) Request to Send (output) >> X >> CTS ( 5) ---------/ \--------- CTS ( 5) Clear to send (input) >> >> DCD ( 8) ---+ +--- DCD ( 8) Carrier Detect (input) >> | | >> DSR ( 6) ---+-----\ /-----+--- DSR ( 6) Data Set Ready (input) >> X >> DTR (20) ---------/ \--------- DTR (20) Terminal Ready (output) >> >> GND ( 7) --------------------- GND ( 7) Signal Ground > > Sorry if this is a silly question, but I have never seen this bit >with pin-8 before (other than straight through) I realise you cross >2/3 4/5 6/20 but I didn't know about this bit with pin-8. There are many ways to make a null modem cable. Some devices only require the simplest forms, others require more elaborate ones. Some null modem wirings may be technically more correct than others, but some devices may require a "less correct" wiring to operate. Unfortunately there is no *one* way to wire a null modem which works everywhere. It depends on the application. As for pin 8, some DTEs (terminals, computers, printers, etc.) require DCD before they'll listen to what's coming over the wire (RD, that is) so you have to make sure it gets asserted. This null modem above asserts DSR and DCD if the remote DTR is asserted. There are other ways to do this which some might consider "better." In anycase, wiring pin 8 straight through makes no sense since pin 8 is an input to a DTE, so you just have the two sides with their "ears" pressed together. ;-) If the device in question needs DCD before proceeding, it won't work. > -Andrew Smith -hans -- Hans-Gabriel Ridder DECwest Engineering, Bellevue, Washington, USA "I'd rather be writing MACRO-20!" Any opinions expressed are not those of my employer, honest.