Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!ucsd!ucbvax!hoptoad!gnu From: gnu@hoptoad.uucp (John Gilmore) Newsgroups: comp.dcom.modems Subject: New "Alternate Connector For Use With ANSI/EIA-232-D" Message-ID: <8539@hoptoad.uucp> Date: 18 Sep 89 03:53:56 GMT References: <870.251007A2@zswamp.fidonet.org> <328@gp.govt.nz> Organization: Grasshopper Group in San Francisco Lines: 99 The standards bogons are at it again. Following on the massive success of the RS-232-C standard (and its followon RS-449 which basically nobody ever adopted), there is a new alternative connector for RS-232-C circuits. Of course, it has even more wires than the current one, though it is physically smaller due to improved connector technology. The new specification is to use a 26-pin version of the "double density" 50-pin SCSI-2 connector. This makes it somewhat smaller than the current DB25 connector, but not much. The spec is simple, you use pins 1-25 the same way they were on DB25's and you don't connect pin 26. This specification is NOT a new standard. It is an "EIA/TIA Telecommunications Systems Bulletin", TSB-26, February 1989. It is four pages long and costs $10 from Electronic Industries Association in Wash, DC. It was prepared by the TR30.2 Subcommittee on Data Transmission Interfaces. It states: "This Technical Bulletin does not constitute a formal change to the standards in question but the information contained herein will be considered in their next revisions...Although the connector presented in the attached drawing is not presently the subject of an American National Standard or an international standard, the values presented reflect current industry agreements." When I read the above I was relieved. THE MISTAKE IS NOT MADE YET! I encourage any and all readers to make sure their companies don't use this connector. What we really need is a SMALL connector with a minimum number of wires. Not a perpetuation of the completely bogus RS-232-C standard. Draft goal spec of new connector: * Cheap and physically small * Easier physical connection than RS-232-C (no little screws) * No options -- make it hard to mis-implement it * No spare pins -- two mfr's can't use them for different things * Connect 90% of data devices without trouble. * (the other 10% can use RS-232-C or RS-449 or something else.) * Provides limited power to local devices like keyboard/mice/modems * Shieldable to reduce RFI (necessary for residential devices) * Uses RS-423 signal levels (RS-232 compatible, and work at higher data rates too) * Compatible with RS-232-C and RS-423 signal levels and definitions so that trivial converter cables can be made * Connectors can be mounted directly on PC Boards (cheap for mfrs) * Mounted connectors provide physical support for small devices (e.g. cigar sized modem could plug right in with no cable). Draft signal spec: GND TX Data RX Data I'm Here (DTR) You're Here (DSR/CD) TX Clock (synchronous modems and flow control) RX Clock (synchronous modems and flow control) +5V, fused and current-limited Simple devices can use GND, TX, RX, maybe 5V. Modems can use I'm Here (DTR) and You're Here (CD). If You're Here goes away, you drop the connection (e.g. host logs people out; modem hangs up phone). I'm Here should reflect software ready status (come on with carrier on phone; come on after software has bootstrapped on host, goes off during crash or power failure). If you need flow control or you are running synchronous, the clock lines are used. If TX Clock is being driven from outside, you use it as your transmitter clock; if the other side needs to flow control you, it stops the clock or slows it down as required. You do the same to the other side by slowing or stopping RX Clock to alter the data flow on your RX Data line. The simple devices and modems would be RS-232 compatible with just a cable. Synchronous modems, ditto. Flow controlled RS-232 devices that can use external clock could be adapted with a matchbox sized device (powered from the connector). Differential TX/RX (AppleTalk, long distance wiring, etc) ditto. There should be no male/female connectors; any connector should fit into any other one. Ideally you could plug it in with a 180 degree rotation to cross the lines (I'm Here <-> You're Here and etc). That way you can not only plug two devices together with a single cable, but you can also extend the length by plugging N cables together -- and if it doesn't work, twist any connector by 180 degrees and plug things back together; now it should work. In other words, if you insert the plug one way, you get straight-thru; the other way you get everything swapped. For this there would have to be two pins of GND and two of power, but that is probably a good idea anyway. The SCSI-2 connector spec'd above does not have this property; it has male and female versions. So even a 10-pin version of it would not be worth writing a new standard for. We should try to interest connector manufacturers in designing one that meets these criteria. -- John Gilmore {sun,pacbell,uunet,pyramid}!hoptoad!gnu gnu@toad.com "Watch me change my world..." -- Liquid Theatre