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Path: utzoo!mnetor!uunet!husc6!cmcl2!brl-adm!adm!art@acc.arpa
From: art@acc.arpa
Newsgroups: comp.unix.questions
Subject: RE: DSR
Message-ID: <8998@brl-adm.ARPA>
Date: Tue, 25-Aug-87 13:53:58 EDT
Article-I.D.: brl-adm.8998
Posted: Tue Aug 25 13:53:58 1987
Date-Received: Wed, 26-Aug-87 06:54:28 EDT
Sender: news@brl-adm.ARPA
Lines: 38


>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?

Data Set Ready basically indicates that the modem is in an operational
state (Data Set is an old Telco term for a modem).  DSR often indicates
that the modem is in data mode rather than voice mode.  DSR can be considered
the counterpart to Data Terminal Ready (DTR), which indicates that the
customer equiptment is ready to operate.  For asynch RS-232 cables,
I recommend the following:


	SD   2 -------------\ /----------------- 2   SD
			     x
	RD   3 -------------/ \----------------- 3   RD

	RTS  4 ---+			    +--- 4   RTS
		  |			    |
	CTS  5 ---+			    +--- 5   CTS

	DSR  6 ---+			    +--- 6   DSR
		  |			    |
	SG   7 ---|-------------------------|--- 7   SG
		  |			    |
	DCD  8 ---o---------\ /-------------o--- 8   DCD
			     x
	DTR 20 -------------/ \----------------- 20  DTR


Art Berggreen
art@acc.arpa

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