RS232 Communication Configuration

	Pin  25-Pin Signal (DTE)	 Pin  9-Pin Signal (DTE)

	  1   Chassis Ground  (GND)	 1   Carrier Detect (CD)
	  2   Transmit Data (TD)	 2   Receive Data (RD)
	  3   Receive Data (RD) 	 3   Transmit Data (TD)
	  4   Request to Send (RTS)	 4   Data Terminal Ready (DTR)
	  5   Clear to Send (CTS)	 5   Signal Ground (SG)
	  6   Data Set Ready (DSR)	 6   Data Set Ready (DSR)
	  7   Signal Ground (SG)	 7   Request to Send (RTS)
	  8   Carrier Detect (CD)	 8   Clear to Send (CTS)
	9-19  (not used)		 9   Ring Indicator (RI)
	 20   Data Terminal Ready (DTR)
	 22   Ring Indicator (RI)

	There are two general cable configurations used with the RS-232C
	Communications Standard:

	  Data Terminal Equipment (DTE): IBM PC's, printers, plotters, etc
	  Data Communication Equipment (DCE): modems, multiplexors, etc

	DCE to DTE requires all lines run straight through
	DTE to DTE usually requires swapping of the following lines

		RD  and TD		RD  and TD
		RTS and CTS	or	RTS,CTS and DCD
		DTR and DSR		DCD and RTS,CTS

	Signal Functions

	GND    Ground		    protective safety ground
	TD     Transmit Data	    DTE output data
	RD     Receive Data	    DTE input data
	RTS    Request To Send	    DTE output, DTE would like to transmit
	CTS    Clear To Send	    DTE input, DCE is ready to transmit
	DSR    Data Set Ready	    DTE input, DCE is ready to communicate
	SG     Signal Ground	    provides a Zero reference voltage
	DCD    Data Carrier Detect  DTE input, data link established, also
				    known as Receive Line Signal Detect (RLSD)
	DTR    Data Terminal Ready  DTE output, device ready
	RI     Ring Indicator	    DTE input, announces incoming call

	- RTS/CTS is used for half duplex line turn around
	- in half duplex DCD is asserted only by the receiving device
	- full duplex modems tie CTS & DCD together (no CTS/RTS handshaking)
	- most modems require DTR to be present to respond to commands
	- maximum voltages are between -15 volts and +15 volts
	- binary outputs are between +5 to +15 volts and -5 to -15 volts
	- binary inputs are between +3 to +15 volts and -3 to -15 volts
	- input voltages between -3 to +3 are undefined while output voltages
	  between -5 and +5 are undefined
	- positive voltages indicate ON or SPACE, negative voltages indicate
	  OFF or MARK