Date: Thu, 14 Jun 2001 14:00:42 -0700 From: Nick Sayer <nsayer@quack.kfu.com> To: Matt Dillon <dillon@earth.backplane.com> Cc: David Miller <dmiller@sparks.net>, freebsd-stable@FreeBSD.ORG Subject: Re: serial port stuck at 9600 Message-ID: <3B2925FA.3040104@quack.kfu.com> References: <Pine.BSF.4.21.0106121330250.59495-100000@search.sparks.net> <200106141948.f5EJmOe28264@earth.backplane.com>
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Matt Dillon wrote: [..] > That is the cable... when building a null modem cable DTR is supposed to > be wired to DCD and vise versa. It should be something like: > > DTR -> DCD > DTR -> DSR > DCD <- DTR > DSR <- DTR > RTS -> CTS > CTS <- RTS > TX -> RX > RX <- TX > SGND<-> SGND > Matt is right, but I will add one aside. I wanted a while ago to make a cable to connect my Ricochet to my Palm. Both have serial ports wired as DCEs instead of DTEs, and a traditional null-modem cable actually didn't work properly. The problem was that in this case the pins actually had the opposite meaning than was expected. So when tying DTEs together, the above is correct. For tying DCEs together, you really don't want a null modem, you really want a "null terminal", I guess, which is a bit more rare. The wiring for that is the same, except that DSR and DTR "cross" from one side to the other in a way no different from RTS and CTS. DCD in this situation is a bit of a question mark, since both sides would presumably want to supply it rather than listen on it. In the scenario involving the Palm, it's a no-brainer, since DCD is not connected to anything on the Palm. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-stable" in the body of the message
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