Subject: Re: Idiots guide to serial ports.
To: Herb Peyerl <>
From: David Maxwell <>
List: netbsd-users
Date: 12/19/2002 11:57:20
On Wed, Dec 18, 2002 at 05:48:34AM -0700, Herb Peyerl wrote:
> "Dr R.S. Brooks" <>  wrote:
>  > Perhaps (as I did some time ago) you bought a so-called null-modem cable
>  > from your local Maplin shop?  AFAIR, the one I got had *most* of the
>  > connections you'd expect, but with one rather important omission:
>  > nothing whatsoever connected to DCD at either end!  I returned it as
>  > misrepresented goods.
> When we were doing documentation for the PC Weasel, we figured we'd
> document the cabling. So we buzzed out the null modem cable we had
> closest to us and found it didn't match our impression of 'null modem
> cable'.  So we rounded up all the ones we had at the office. We also
> drove around town and bought one of each 'brand' of null modem cable
> and adapter we could find.  Only one place had what we considered to
> be a true null modem cable.  But we did manage to find 6 different
> renditions of 'null modem', only one of which had DCD connected.

It is a shame serial cables and port requirements differ so greatly.
I've spent too many hours of my life trying to figure out what signals a
device wanted to see before it would communicate.

I've found this device to be quite handy for debugging:

Part 8202 is a cheap in-line switch that lets you try 18 types of cable
configurations quickly.

David Maxwell,| -->
An organization gets what it rewards.
			      - Perry Metzger