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From: german@uiucuxc.Uiuc.ARPA
Newsgroups: net.micro.pc
Subject: Re: IBM AT Serial Line Pinouts
Message-ID: <21900070@uiucuxc>
Date: Sat, 24-Aug-85 11:45:00 EDT
Article-I.D.: uiucuxc.21900070
Posted: Sat Aug 24 11:45:00 1985
Date-Received: Mon, 26-Aug-85 01:18:28 EDT
References: <2077@ukma.UUCP>
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Nf-From: uiucuxc.Uiuc.ARPA!german    Aug 24 10:45:00 1985


It has been awhile since this information was last posted to the net so
here it goes:

The IBM PC AT Serial/Parallel Adapter has a 9-pin D shell type
connector which is configured as follows:

       Pin	Signal Name (DCE)     RS-232C Pin (DCE)
      -----    --------------------  -------------------
	1	Carrier Detect		 8 (CD)
	2	Received Data		 3 (RD)
	3	Transmitted Date	 2 (TD)
	4	Data Terminal Ready	20 (DTR)
	5	Signal Ground		 7 (SG)
	6	Data Set Ready		 6 (DSR)
	7	Request To Send		 4 (RTS)
	8	Clear To Send		 5 (CTS)
	9	Ring Indicate		22 (RI)

The above is for attachment to Data Communications Equipment such as a
modem.  To attach to another terminal (DTE) device the following signal
lines must be changed:

       Pin	Signal Name (DCE)     RS-232C Pin (DTE)
      -----    --------------------  -------------------
	2	Recieved Data		 2 (TD)    (RD & TD Swapped)
	3	Transmitted Data	 3 (RD)
	4	Data Terminal Ready	 6 (DSR)   (DTR & DSR Swapped)
	6	Data Set Ready		20 (DTR)
      / 7	Request To Send		 4 (CTS) \ (Pins jumpered together at
      \ 8	Clear To Send		 5 (RTS) / each end only in pairs. Pin
						   7 to 8, 4 to 5. Not needed
						   for Full-Duplex operation.)

This information may be obtained from the IBM Technical Reference,
Options and Adapters Mannual, Volume 2 after installing update pages
which are actually provided in the Technical Reference, Personal
Computer AT Mannual.  This means you need the AT tech ref to get the
specification if you haven't already obtained one.