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From: peter@aragorn.OZ (Peter Horan)
Newsgroups: comp.sys.mac
Subject: Re: Mac+ DTR upside down?
Message-ID: <298@aragorn.OZ>
Date: Wed, 26-Nov-86 23:48:58 EST
Article-I.D.: aragorn.298
Posted: Wed Nov 26 23:48:58 1986
Date-Received: Thu, 27-Nov-86 07:59:16 EST
References: <1372@umd5> <3897@nsc.NSC.COM>
Reply-To: peter@aragorn.UUCP (Peter Horan)
Distribution: net
Organization: Division of Comp/Maths, Deakin Uni., Australia
Lines: 22

In article <3897@nsc.NSC.COM> curry@nsc.UUCP (Ray Curry) writes:
>Don't forget that the rs232/rs422 world defines their signals as active (DTR)
>but the lines are all physical (DTR-).  DTR- line being held low is active.

This is not correct for control lines like DTR.
From the standard EIA RS232C Aug 1969:

Notation		Interchange Voltage
		Negative		Positive
Binary State	    1			    0
Signal Condition  Marking		Spacing		{the data lines}
Function	  OFF			  ON		{lines like DTR}

So data lines are negative logic, whereas control lines are positive
logic.

Peter Horan				ACSnet: peter@aragorn.oz
Division of Computing and Mathematics   UUCP: {seismo,ukc,mcvax}!munnari!
Deakin University				aragorn!peter
Geelong					ARPA: peter%aragorn.oz@seismo.edu.gov
Victoria				+61 52 471234
Australia 3217				(052) 471234