ridder@elvira.cxo3.dec.com (Hans Ridder) (12/02/89)
In article <845@lpami.wimsey.bc.ca> lphillips@lpami.wimsey.bc.ca (Larry Phillips) writes: >While I'm at it, I may as well voice my pet peeve about connectors. >IBM did the RS-232 WRONG. I know it isn't in the spec, but up until >these clowns got hold of it, most manufacturers used FEMALE connectors >on their equipment (not as easy to short out). Now we have CBM, who >did it right on the A1000, then decided to kowtow to the IBMishness >and use a male RS-232. Grr. Oh no! Not the RS-232 gender wars again!?! Let's see if we can nip this one in the bud. RS-232 (now EIA-232) has, for quite a while specified the gender of connectors. My copy of the standard, dated August 1969, says it on page 7 section 3.1. The language is a bit difficult, but is basically gets around to saying that female connectors are for DCE's (modems), and male connectors are for DTE's (terminals and to most people, computers). So, IBM followed the standard, not the bandwagon. #define SOAPBOX DEC has done it this way for as long as I can remember, and the result is that for most situations only one of two types of cables is required: either a null-modem with female connectors on both ends, or a straight cable with one male and one female connector. Around here, it's almost impossible to find any "gender menders" or the like. If the cable mates with the connectors, it's the right one (sync. vs. async. not withstanding.) #endif SOAPBOX I probably should have avoided the soapbox when I was trying to end a discussion, but I couldn't help myself....:-) >-larry > -hans ======================================================================== Hans-Gabriel Ridder Digital Equipment Corporation ridder@elvira.enet.dec.com Customer Support Center ...decwrl!elvira.enet!ridder Colorado Springs, CO
lphillips@lpami.wimsey.bc.ca (Larry Phillips) (12/02/89)
In <503@shodha.dec.com>, ridder@elvira.cxo3.dec.com (Hans Ridder) writes: >RS-232 (now EIA-232) has, for quite a while specified the gender of >connectors. My copy of the standard, dated August 1969, says it on >page 7 section 3.1. The language is a bit difficult, but is basically >gets around to saying that female connectors are for DCE's (modems), >and male connectors are for DTE's (terminals and to most people, >computers). So, IBM followed the standard, not the bandwagon. The last time I read the spec, which was when I made a statement about the gender issue, and was corrected, it did not state the gender for the DTE. I would be interested in knowing if your copy of the spec actually says that or if you are just choosing to interpret it that way. I am not interested in gender wars. I am interested in facts. -larry -- " All I ask of my body is that it carry around my head." - Thomas Alva Edison - +-----------------------------------------------------------------------+ | // Larry Phillips | | \X/ lphillips@lpami.wimsey.bc.ca -or- uunet!van-bc!lpami!lphillips | | COMPUSERVE: 76703,4322 -or- 76703.4322@compuserve.com | +-----------------------------------------------------------------------+
doug@xdos.UUCP (Doug Merritt) (12/04/89)
In article <856@lpami.wimsey.bc.ca> lphillips@lpami.wimsey.bc.ca (Larry Phillips) writes: >I am not interested in gender wars. I am interested in facts. This should've been posted to e.g. soc.women. :-) :-) :-) Doug -- Doug Merritt {pyramid,apple}!xdos!doug Member, Crusaders for a Better Tomorrow Professional Wildeyed Visionary
lphillips@lpami.wimsey.bc.ca (Larry Phillips) (12/05/89)
In <511@shodha.dec.com>, ridder@elvira.cxo3.dec.com (Hans Ridder) writes: > > [ chunk of EIA-232 and some comments deleted ] > >What I find bizzare here is this concept of an "extension" cable on >the DTE. Heck, even the DCE connector "mounted in a fixed position >near the DTE" is a pretty strange concept. I *believe* they were >thinking that all DTE's would have a cable coming out of them with a >male connector on the free end. Sort of like the old DEC LA36's and >VT52's had. And that *some* DCE's might have such a cable too. Right. Or sort of. I believe (and of course this is my own interpretation) that the spec is specifically talking about the DCE only, and that there is really no reference to the DTE, except in relation to the DCE itself. >You're right, they never get right down and say "the male connector >shall be associated with the DTE". But they do say that the DTE will >be provided with a cable with a male connector. I would say that the >connector mounted directly on the DTE is just the special case of a >zero length "extension" cable. That, and the stuff in section 3.1.1 >about connectors on "inserted" units sure makes me think they intended >male connectors to be on DTE's or DTE-like equipment. That's what I figured. Thing is.. regardless of the lack of spcifics in defining the gender on the DTE itself, virtually all companies (before IBM inflicted their PC on the industry), interpreted the spec as being open about said gender, and most used female on the DTE. >Anyway, I can certainly see that the words are ambiguous, or at least >open to some interpretation. Aren't standards wonderful? You'd think >they would clarify things like this, but nooooooooo. By the way, is >the text in your copy of the spec any different? <sigh> Yup. It never fails to amaze me that a standards committee could overlook something like this, while never forgetting to write in such things as load capacitance, and writing it in ways that require the engineering equivalent of a Philly lawyer. It's almost as if the entire committee was composed of engineers living in a vacuum, and that nobody from the real world had anything to say about it at all. That's the same text as appeared in the spec I read. Thanks for the discussion, and for refreshing my memory on it. -larry -- " All I ask of my body is that it carry around my head." - Thomas Alva Edison - +-----------------------------------------------------------------------+ | // Larry Phillips | | \X/ lphillips@lpami.wimsey.bc.ca -or- uunet!van-bc!lpami!lphillips | | COMPUSERVE: 76703,4322 -or- 76703.4322@compuserve.com | +-----------------------------------------------------------------------+
ridder@elvira.cxo3.dec.com (Hans Ridder) (12/05/89)
To: lphillips@lpami.wimsey.bc.ca Subject: Re: RS232 gender (was Re: Apple SCSI not compatible with standard SCSI?) Newsgroups: comp.sys.amiga.tech In-Reply-To: <856@lpami.wimsey.bc.ca> Organization: Digital Equipment Corporation, Customer Support Center Cc: Bcc: In article <856@lpami.wimsey.bc.ca>, lphillips@lpami.wimsey.bc.ca writes: >In <503@shodha.dec.com>, ridder@elvira.cxo3.dec.com (Hans Ridder) writes: >>RS-232 (now EIA-232) has, for quite a while specified the gender of >>connectors.... [my interpretation of EIA-232 deleted] > >The last time I read the spec, which was when I made a statement about the >gender issue, and was corrected, it did not state the gender for the DTE. I >would be interested in knowing if your copyof the spec actually says that or >if you are just choosing to interpret it that way. Well, to a certain extent I was reading what I wanted to see. I've been reading alot of RS-449 and EIA-530 lately and they specify the DCE *and* DTE connector clearly. Anyway, the *exact* text in my copy (probably the same as yours) says: (The following is copyright 1981 Electronic Industries Association, included without permission. Though I don't think they mind) "3.1 The interface between the data terminal equipment and data communication equipment is located at a pluggable connector signal interface point between the two equipments. The female connector shall be associated with, but not necessarily physically attached to the data communications equipment and should be mounted in a fixed position near the data terminal equipment. The use of an extension cable on the data communication equipment is permitted. An extension cable with male connector shall be provided with the data terminal equipment. The use of short cables (each less than approximately 50 feet or 15 meters) is recommended; however, longer cables are permissible, provided that the resulting load capacitance (C(L) of Fig. 2.1), measured at the interface point and including the signal terminator, does not exceed 2500 picofarads. (See section 2.4 and 6.5.) 3.1.1 When additional functions are provided in a separate unit inserted between the data terminal equipment and the data communication equipment (See section 1.7), the female connector, as indicated above shall be associated with the side of this unit which interfaces with with the data terminal equipment while the extension cable with the male connector shall be provided on the side which interfaces with the data communications equipment." What I find bizzare here is this concept of an "extension" cable on the DTE. Heck, even the DCE connector "mounted in a fixed position near the DTE" is a pretty strange concept. I *believe* they were thinking that all DTE's would have a cable coming out of them with a male connector on the free end. Sort of like the old DEC LA36's and VT52's had. And that *some* DCE's might have such a cable too. You're right, they never get right down and say "the male connector shall be associated with the DTE". But they do say that the DTE will be provided with a cable with a male connector. I would say that the connector mounted directly on the DTE is just the special case of a zero length "extension" cable. That, and the stuff in section 3.1.1 about connectors on "inserted" units sure makes me think they intended male connectors to be on DTE's or DTE-like equipment. Anyway, I can certainly see that the words are ambiguous, or at least open to some interpretation. Aren't standards wonderful? You'd think they would clarify things like this, but nooooooooo. By the way, is the text in your copy of the spec any different? >I am not interested in gender wars. I am interested in facts. > >-larry Neither am I. Scouts honor, I was trying to head off a war. I hope I didn't start one though.... :-) -hans ======================================================================== Hans-Gabriel Ridder Digital Equipment Corporation ridder@elvira.enet.dec.com Customer Support Center ...decwrl!elvira.enet!ridder Colorado Springs, CO
jms@tardis.Tymnet.COM (Joe Smith) (12/06/89)
In article <503@shodha.dec.com> ridder@elvira.cxo3.dec.com (Hans Ridder) writes: >RS-232 (now EIA-232) has, for quite a while specified the gender of >connectors. My copy of the standard, dated August 1969, says it on >page 7 section 3.1. The language is a bit difficult, but is basically >gets around to saying that female connectors are for DCE's (modems), >and male connectors are for DTE's (terminals and to most people, >computers). So, IBM followed the standard, not the bandwagon. Yes. It was really simple back then. All terminals had male connectors at the end of permanently attached 6-foot cables, and all modems have female connectors mounted on the box. We had plenty of hassles when our computing center upgraded to terminals came without cables attached. Too many people assumed the standard was "male on cables, female on chassis" instead of "male on terminals, female on whatever the terminal plugs in to". -- Joe Smith (408)922-6220 | SMTP: JMS@F74.TYMNET.COM or jms@gemini.tymnet.com BT Tymnet Net Tech Serv | UUCP: ...!{ames,pyramid}!oliveb!tymix!tardis!jms PO Box 49019, MS-D21 | PDP-10 support: My car's license plate is "POPJ P," San Jose, CA 95161-9019 | humorous dislaimer: "My Amiga speaks for me."
stephen@hpdml93.HP.COM (Stephen Holmstead) (12/08/89)
Keith Hanlan writes: >What is meant by "differential SCSI"? >What is meant by "single-ended SCSI"? These are two options on types of signals on the SCSI bus. Single-ended SCSI signals change between +5v and GND, whereas differential SCSI signals change between +12v and -12v. Thus, on single-ended SCSI, half of the pins are grounds, whereas they are -12v returns in differential SCSI. Q: Why do we have single-ended and differential options? A: To confuse people. :-) A2: Because differential SCSI, although more expensive, can have longer cables and faster data rates. Some people can't get by with the 6 meter cable limit on single-ended SCSI. 1/2 :-) (This doesn't really apply to personal computers, but it does make sense if you think about a computer lab environment with BIG computers). - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Stephen Holmstead Hewlett Packard Disk Mechanism Division ...!hplabs!hpdmlge!stephen // stephen@hpdmlge.boi.hp.com \X/ Amiga Forever!
charles@hpcvca.CV.HP.COM (Charles Brown) (12/12/89)
>> Differential drive is a technique of sending signals to eliminate >> noise. You use two wires for each signal. One wire carries the >> normal signal, and the other wire carries the signal after being >> inverted. At the recieving end, you invert the signal that was >> inverted at the transmiter, and add them together. Any noise on the >> line cancels out (since each line gets the same amount of noise >> placed on it during the traversal of the cable) and you end up with >> a clean signal. >> (david williams) > Not quite. Adding the inversion of the inverted signal to the positive > signal will result in the doubling of the amplitude of the signal. > However, the noise is in no way eliminated. It too in fact increseas > in magnitude, but does not double because it is random by nature. That > means that some times you get spikes which are as high as double in > usual magnitude, and sometimes you get lucky ang get a cancel out. > Valentin Most of the noise that shows up in cables is EMI induced. Thus it is not random. In practice noise is coupled (almost) equally into both differential lines. (Differential wires are frequently twisted to encourage this. They are then called a twisted pair.) So the noise DOES cancel at the receiver. This discussion is drifting from any relevance to the Amiga. Perhaps we should just drop it. (Maybe I should have already dropped it. ;-) -- Charles Brown charles@cv.hp.com or charles%hpcvca@hplabs.hp.com or hplabs!hpcvca!charles or "Hey you!" Not representing my employer.