HP 5M manual Pin Functions

	Pin Functions
Pin 1-	This pin is also referred to as chassis ground and should not be confused with pin 7, or common
Protective Ground	ground which serves as the circuit common. The purposed of this pin is to provide protection
	against electrical shock where two pieces of equipment are connected and one piece does not
	include a ground connection, or round prong on its AC plug. In some cases not connecting
	chassis ground may disable communication or connecting these pins may create a problem
	known as a ground loop. Both of these situations are rare in general and in most cases pin 1 is
	not needed to establish communication between two devices. Questions regarding the need for
	connecting or not connecting chassis ground should be referred to an electrical expert.
Pin 2-	This pin transmits data.
Transmitted Data
(TxD or TD)
Pin 3-	This pin receives data.
Received Data
(RxD or RD)
Pin 4-	General purpose output. Uses vary widely. In half-duplex modems this is used to signal a desire
Request to Send	to transmit data.
(RTS)
Pin 5-	General purpose input. Uses vary widely. In half-duplex modems this is used to grant permission
Clear to Send (CTS)	to transmit.
Pin 6-	General purpose input to signal that the DTE and the DCE is powered up and ready to go.
Data Set Ready
(DSR)
Pin 7-	Reference point for all interface voltages.
Common
Pin 8-	On modems DCD is asserted when connected to a remote modem. On a DTE it is frequently
Data Carrier Detect	used to disable data reception.
(DCD)
Pin 20-	General purpose output. Generally used to signal to the DCE that the DTE has been powered up
Data Terminal	and is ready to go.
Ready (DTR)

E-4 Serial Pin-out and Cabling Configuration

EN