Serial port pins configuration

About Serial Ports.

By: Pratik Solanki

Serial Pinouts (D25 and D9 Connectors)

D-Type-25 Pin No.	D-Type-9 Pin No.	Abbreviation	Full Name
Pin 2	Pin 3	TD	Transmit Data
Pin 3	Pin 2	RD	Receive Data
Pin 4	Pin 7	RTS	Request To Send
Pin 5	Pin 8	CTS	Clear To Send
Pin 6	Pin 6	DSR	Data Set Ready
Pin 7	Pin 5	SG	Signal Ground
Pin 8	Pin 1	CD	Carrier Detect
Pin 20	Pin 4	DTR	Data Terminal Ready
Pin 22	Pin 9	RI	Ring Indicator

Table 1 : D Type 9 Pin and D Type 25 Pin Connectors
Pin Functions

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	Abbreviation		Full Name	Function
		TD	Transmit Data	Serial Data Output (TXD)
		RD	Receive Data	Serial Data Input (RXD)
		CTS	Clear to Send	This line indicates that the Modem is ready to exchange data.
		DCD	Data Carrier Detect	When the modem detects a "Carrier" from the modem at the other end of the phone line, this Line becomes active.
		DSR	Data Set Ready	This tells the UART that the modem is ready to establish a link.
		DTR	Data Terminal Ready	This is the opposite to DSR. This tells the Modem that the UART is ready to link.
		RTS	Request To Send	This line informs the Modem that the UART is ready to exchange data.
		RI	Ring Indicator	Goes active when modem detects a ringing signal from the PSTN.

Null Modems

A Null Modem is used to connect two DTE's together. This is commonly used as a cheap way to network games or to transfer files between computers using Zmodem Protocol, Xmodem Protocol etc. This can also be used with many Microprocessor Development Systems.