wall@fortune.UUCP (11/07/83)
Ah, yes; lets be gentle with me for surely I have lost my marbles and most obviosly have no real knowlege of data communication. But lets really see what is going on here. There is no doubt that the RS232 spec. does not refer to DTR as being used as a handshake signal. No problem with that. Unfortunately, the specification also insists that only modems be DCE devices. Now, I hate to be the one to break this news to you, but that is just not the way the real world choose to use the standard. Almost all computers from the small through the desk-top size, all the way up to the big boys have DCE outputs so that they may talk to terminals and printers directly without having to use null modem cables. Any objections? I would rather that DEC and IBM have never started this trend of corrupting the spec., but it happened and is just as much a part of the standard as is what is printed. Now, lets look at the definition of the DTR signal Data Terminal Ready. Normally used to control the -switching- of the DCE device to the comm channel, the bottom line being the controlling of the data flow whenever the DTE is not ready to send or receive data. Now, if a DCE (read direct connected computer) is sending data to a DTE faster than it can accept the data, the only, and I repeat the only, hardware meathod available for flow control is to use DTR. And it makes sense doesn't it? Dropping the Data Terminal Ready line to indicate that it is not ready to recieve any more data. Enough said, I'm tired of defending what virtually every terminal and computer manufacturer today do as standard. I haven't said anything about software flow control, and it works as well for most cases, but using hardware flow control from the DTE up to the DCE is real, and I'm sorry, but it isn't just !fortune!wall that is doing it. Sorry for the tone of the message. But it took a long time and training to learn the many varied aspects of this poor misused spec. and just because someone read the words on paper isn't just cause to throw down on me. -Jim
jhh@ihldt.UUCP (11/08/83)
I haven't looked at all of their products, but DEC definitely has a male connector on the DZ-11, KMS-11, and other products. They do not, however, supply the cable required of DTEs, but the connector is wired as a DTE, so that modems can be connected directly to their distribution panel with a 25 wire straight through cable. They do manufacture null modem cables. John Haller
phil@amd70.UUCP (11/08/83)
Jim, if "fortune" is a VAX then, like my PDP-11, it probably has a DH-11
type serial interface, which is DTE, not DCE. It even has male connectors.
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Phil Ngai (408) 988-7777 {ucbvax|decwrl|ihnp4|allegra}!amd70!phil