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From: jfh@killer.UUCP (The Beach Bum)
Newsgroups: comp.unix.questions
Subject: Re: The DSR pin - what is it used for?
Message-ID: <1411@killer.UUCP>
Date: Wed, 26-Aug-87 15:46:13 EDT
Article-I.D.: killer.1411
Posted: Wed Aug 26 15:46:13 1987
Date-Received: Sat, 29-Aug-87 09:26:09 EDT
References: <304@pvab.UUCP>
Organization: Big "D" Home for Wayward Hackers
Lines: 67
Summary: List of what they do's

In article <304@pvab.UUCP>, robert@pvab.UUCP (Robert Claeson) writes:
> This is maybe a dumb question, but what is the intended use of pin 6,
> the one named DSR or Data Set Ready in the RS232 standard? I've seen
> that some devices (especially modems) uses it, but most ignores it (such
> as computers and terminals). Is it really needed for modem-control
> signaling or can I simply connect it to pin 20 (DTR) at the other end?
> How should it be connected in a null-modem cable when I want to connect
> two DTE devices with modem control?

Below is the copy of a file I keep around for cable building.  It lists the
most common signals on a RS-232 DB-25 connector for Data Terminal Equipment.

Might do you some good to save a copy of this file (maybe as /usr/pub/rs232)

CONNECTOR SIGNALS

DTE Wired Equipment

 1 - Chassis Ground
 2 - Transmit Data		(output)
 3 - Receive Data		(input)
 4 - Request to Send		(output)
 5 - Clear to Send		(input)
 6 - Data Set Ready		(input)
 7 - Signal Ground
 8 - Carrier Detect		(input)
20 - Data Terminal Ready	(output)

As you can see, DSR is an input signal.  What normally goes on with this
signal is you connect it to DCD for a modem (least ways I do) or DTR for
a terminal.

MULTIPLEXOR to PLEXUS P/60 CABLE

P l e x u s   P / 6 0       M u l t i p l e x o r

2   -----------------------------------------   3

3   -----------------------------------------   2

4   -----------------------------------------   5

6   -----------------------------------------  20

7   -----------------------------------------   7

20  -----------------------------------------   6

This would be how I would connect a Case Multiplexor Port to a serial
port on the P/60 (The one we are getting rid of :-).  Basically, RxD
and TxD are swapped and DTR and DSR are also swapped.  This works
pretty well.

One big suggetion - once you find a cable wiring that works, save it
in a file someplace public (unless only you make cables at your site)
so that the rest of the world won't have to go through the grief of
figuring out how to wire an IBM/PC to an HP Plotter.  Identifying
equipment as DTE or DCE make swapping the numbers alot easier.

---------- END OF `CABLE IN COMPUTER SCIENCE' 101 --------

John.
-- 
John F. Haugh II		HECI Exploration Co. Inc.
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