EIA-232 (formerly known as RS-232) pinouts

[Dave Loucks]

25-pin EIA-232 Port



   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   

Pin No.	Name	Dir	Notes/Description
1	PGND	IN	Protective ground.  Cable shield connected here.
2	TD	OUT	Transmit Data (a.k.a TxD, Tx). Sending data to DCE from DTE.
3	RD	IN	Receive Data (a.k.a RxD, Rx). Arriving data from DCE.
4	RTS	OUT	Request to Send.  Raised by DTE when it wishes to send.  Expects CTS from DCE.
5	CTS	IN	Clear to Send. Raised by DCE in response to RTS from DTE
6	DSR	IN	Data Set Ready. Raised by DCE to indicate ready.
7	SGND	-	Signal ground / common for all other signals.
8	DCD	IN	Data Carrier Detect. Raised by DCE when modem synchronized.
9	+	OUT	+VOLTAGE.  Defined but typically not implemented.
10	-	OUT	-VOLTAGE.  Defined but typically not implemented.
11	-	-	Unassigned pin.  No connection.
12	sDCD	IN	Secondary Data Carrier Detect (or Received Line Signal Detector)
13	sCTS	IN	Secondary Clear To Send.
14	sTD	OUT	Secondary Transmit Data (sTxD).
15	TSET	IN	Transmitter Signal Element Timing.
16	sRD	IN	Secondary Received Data (sRxD).
17	RSET	IN	Receiver Signal Element Timing.
18	LL	OUT	Local Loopback.
19	sRTS	OUT	Secondary Request To Send.
20	DTR	OUT	Data Terminal Ready.  Typically raised when the data terminal (PC or PLC) is powered and ready.
21	RL	OUT	Remote Loopback.
22	RI	IN	Ring Indicate.  Raised by DCE and sent to DTE to tell DTE to get ready... a call is coming.
23	sCTS	-	Data Signal Rate Selector. Can sent by either DCE or DTE.
24	ETSET	OUT	External Transmit Signal Element Timing.
25	TM	IN	Test Mode.

9-pin EIA-232 Port



   
   
   
   
   
   
   
   
   
   

Pin No.	Name	Dir	Notes/Description
1	DCD	IN	Data Carrier Detect. Raised by DCE when modem synchronized.
2	RD	IN	Receive Data (a.k.a RxD, Rx). Arriving data from DCE.
3	TD	OUT	Transmit Data (a.k.a TxD, Tx). Sending data from DTE.
4	DTR	OUT	Data Terminal Ready. Raised by DTE when powered on. In auto-answer mode raised only when RI arrives from DCE.
5	SGND	-	Ground
6	DSR	IN	Data Set Ready. Raised by DCE to indicate ready.
7	RTS	OUT	Request To Send. Raised by DTE when it wishes to send. Expects CTS from DCE.
8	CTS	IN	Clear To Send. Raised by DCE in response to RTS from DTE.
9	RI	IN	Ring Indicator. Set when incoming ring detected - used for auto-answer application. DTE raised DTR to answer.