http://www.bmcc.cc.or.us/ts/hardware/plotter/7475a.shtml
Plotter				Computer
----------------------------------------------------------- 25 to 25 pin
Protective Ground	1----1	Protective Ground
Transmit Data		2----3	Receive Data
Receive Data		3----2	Transmit Data
Signal Ground		7----7	Signal Ground
Data Terminal Ready	20----5	Clear To Send
			|--6	Data Set Ready
			5----20
			6--|
----------------------------------------------------------- 25 to 9 pin
Plotter				Computer
Request To Send		4----1	Received Line Signal Detect
Transmit Data		2----2	Receive Data
Receive Data		3----3	Transmit Data
Clear To Send		5----4	Data Terminal Ready
Data Set Ready		6--| 
Signal Ground		7----5	Signal Ground
Data Terminal Ready	20----6	Data Set Ready
			|--8	Clear To Send
Data Carrier Detect	8----7	Request To Send

echo "IN;SP1;PA0,0;PD1000,1000;SP0;PG;" > /dev/ttyS1