Epson 4100 manual Pair Pin Clear to Send

B-6 Appendix B—Serial Interface

With the exception of Frame Ground and Signal Ground, the nine signals can be categorized as data signals or control signals and are paired as shown below:

Data Signal Pair:	Pin 2	Transmitted Data	TxD
	Pin 3	Received Data	RxD
Control Signal	Pin 4	Request to Send	RTS
Pair:	Pin 5	Clear to Send	CTS
Control Signal	Pin 6	Data Set Ready	DSR
Pair:	Pin 20	Data Term.	DTR
		Ready

Pin 8, Data Carrier Detect, is also a control signal but it does not have a functional pair. Some situations require a high voltage on this input to allow communication. See "Making a Serial Cable" on Page B-9.