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From: ad0@pucc-i (Andy Thomas)
Newsgroups: net.micro.pc
Subject: Re: Homemade AT Serial Port/RS232 Cable - (nf)
Message-ID: <816@pucc-i>
Date: Mon, 14-Jan-85 16:21:58 EST
Article-I.D.: pucc-i.816
Posted: Mon Jan 14 16:21:58 1985
Date-Received: Tue, 15-Jan-85 02:34:06 EST
References: <5100034@uiucdcsb.UUCP>
Organization: Purdue University Computing Center
Lines: 72


   Here are the pin assignments of the 9 pin D connector on the
IBM PC/AT serial port.

	Pin	Description		Signal Source
	---	-----------		-------------
	1	Carrier Detect 		modem
	2	Receive Data   		modem
	3	Transmit Data  		PC/AT
	4	Data Terminal Re	PC/AT
	5	Signal Ground
	6	Data Set Ready		modem
	7	Request to Send 	PC/AT
	8	Clear to Send		modem
	9	Ring In			modem


   Here are the RS-232 Signal Conventions
					
	Pin	Description		Signal Source
	---	-----------		-------------
	2	Trensmitted Data	Terminal
	3	Received Data		Modem

	4	Request to Send		Terminal
	5	Clear to Send		Modem
	6	Data Set Ready		Modem
	8	Carrier Detect		Modem
	20	Data Terminal Ready	Terminal
	22	Ring Indicator		Modem

	7	Signal Ground


If you want to use the control signals, you could try the following cable:

	DB-9 Pin	Description		DB-25 Pin
	--------	-----------		---------
	1		Carrier Detect		8
	2		Tramsmit Data		3
	3		Received Data		2
	4		Data Terminal Rdy	20
	5		Ground			7
	6		Data Set Ready		6
	7		Request to Send		4
	8		Clear to Send		5
	9		Ring Indicator		22

To use a cable with no control signals (known as a null modem cable) try
the following:

	DB-9 Pin	Description		DB-25 Pin
	--------	-----------		---------
	2		Tramsmit Data		3
	3		Received Data		2
	5		Ground			7
	
	DB-9 : Wire pins 7&8 together
	       Wire pins 1,6,&4 together

					DB-25 : Wire pins 6,8,&20 together
						Wire pins 4&5 together



   I have not tried these cables yet, but am sure they will work.

					Andrew Thomas
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