RS232 Cables and Wiring

RS232 Wiring Stuff

RS232 standards are defined by EIA/TIA (Electronic Industries Alliance /Telecommunications Industry Association). RS232 defines both the physical and electrical characteristics of the interface. RS232 is practically identical to ITU V.24 (signal description and names) and V.28 (electrical). RS232 is an Active LOW voltage driven interface and operates at +12V to -12V where:

Signal = 0 (LOW) > +3.0V

Signal = 1 (HIGH) < -3.0V

Signal voltages in the range >-3.0V to +3.0V is regarded as the 'dead area' and allows for absorption of noise. For more on this stuff go here.

Watch the terms DTE (Data Terminal Equipment - e.g. a terminal or PC) and DCE (Data communications Equipment - e.g. a modem) the meaning and use of certain pins may differ. All the diagrams below define the interface from the DTE perspective. An RS232 interface has a female and male connector, the male connector has got the bits sticking out!!

NOTE: The terms Data Carrier Detect (DCD) and Received Line Signal Detect (RLSD) are one and the same. We use DCD throughout 'cos we think its more common.

Contents

RS232 on DB25 Pinout (RS-232C)

RS232 on DB9 Pinout (EIA/TIA - 574)

RS232 on RJ45 (RS-232D EIA/TIA-561)

RS232 DB25 NULL Modem Pinout

RS232 DB9 NULL Modem Pinout

RS232 DB9 to DB25 Pinout

RS232 DB9 to DB25 NULL Modem Pinout

V.35 on a DB25 (EIA/TIA RS-530-A)

RS232 on DB25 (RS-232C)

Signal/pin primer

Pin No.	Name	Notes/Description
1	-	Protective/shielded ground
2	TD	Transmit Data (a.k.a TxD, Tx)
3	RD	Receive Data (a.k.a RxD, Rx)
4	RTS	Request To Send
5	CTS	Clear To Send
6	DSR	Data Set Ready
7	SGND	Signal Ground
8	CD	Carrier Detect (a.k.a DCD)
9	-	Reserved for data set testing
10	-	Reserved for data set testing
11	-	Unassigned
12	SDCD	Secondary Carrier Detect
13	SCTS	Secondary Clear to send
14	STD	Secondary Transmit Data
15	DB	Transmit Clock (a.k.a TCLK, TxCLK)
16	SRD	Secondary Receive Data
17	DD	Receive Clock (a.k.a. RCLK)
18	LL	Local Loopback
19	SRTS	Secondary Request to Send
20	DTR	Data Terminal Ready
21	RL/SQ	Signal Quality Detector/Remote loopback
22	RI	Ring Indicator (DCE raises when incoming call detected used for auto answer applications)
23	CH/CI	Signal Rate selector
24	DA	Auxiliary Clock (a.k.a. ACLK)
25	-	Unassigned

view - looking into male connector

RS232 on DB9 (EIA/TIA 574)

Signal/pin primer

Pin No.	Name	Notes/Description
1	DCD	Data Carrier Detect
2	RD	Receive Data (a.k.a RxD, Rx)
3	TD	Transmit Data (a.k.a TxD, Tx)
4	DTR	Data Terminal Ready
5	SGND	Ground
6	DSR	Data Set Ready
7	RTS	Request To Send
8	CTS	Clear To Send
9	RI	Ring Indicator

View - looking into male connector

RS232 on RJ45 (RS-232D)

More properly EIA/TIA - 561. Use when connecting to or from a serial port with a 8 position Modular Jack (RJ45). If you are cross-connecting from a DB9 or a DB25 use the signal names to cross connect the appropriate connections.

Signal/pin primer

Pin No.	Name	Notes/Description
1	DSR/RI	Data set Ready/ring indicator
2	DCD	Data Carrier Detect
3	DTR	Data Terminal Ready
4	SGND	Signal Ground
5	RD	Receive Data
6	TD	Transmit Data
7	CTS	Clear to Send
8	RTS	Request to Send

RJ45 Male Connector Pin Numbering

RS232 DB25 NULL Modem Pinout

Use when connecting two systems (e.g. PCs) via their DB25 interfaces without a modem (i.e. back-to-back). See the full signal names in the DB25 sections.

Signal/pin primer

DB25	Signal	DB25	Signal
3	RD	2	TD
2	TD	3	RD
20	DTR	6,8	DSR, DCD
6,8	DSR, DCD	20	DTR
4	RTS	5	CTS
5	CTS	4	RTS<
7	SGND	7	SGND
22	RI	22	RI

NOTE: Leave all pins not specified above unconnected.

RS232 DB9 NULL Modem Pinout

Use when connecting two systems (e.g. PCs) via their DB9 interfaces without a modem (i.e. back-to-back). See the full signal names in the DB9 section.

Signal/pin primer

DB9	Signal	DB9	Signal
2	RD	3	TD
3	TD	2	RD
4	DTR	6,1	DSR, DCD
6,1	DSR, DCD	4	DTR
7	RTS	8	CTS
8	CTS	7	RTS
5	SGND	5	SGND
9	RI	9	RI

NOTE: Leave all pins not specified above unconnected.

RS232 DB9 to DB25 Pinout

Use when connecting a DB9 (e.g. a PC) to a DB25 (e.g. a modem) interface. See the full signal names in the DB9 and DB25 section.

Signal/pin primer

DB9	Signal	DB25
1	DCD	8
2	RD	3
3	TD	2
4	DTR	20
5	SGND	7
6	DSR	6
7	RTS	4
8	CTS	5
9	RI	22

RS232 DB9 to DB25 NULL Modem Pinout

Use when connecting two systems (e.g. PCs) when one has a DB9 interface and the other a DB25 interface without a modem (i.e. back-to-back). See the full signal names in the DB9 and DB25 sections.

Signal/pin primer

DB9	Signal	DB25	Signal
2	RD	2	TD
3	TD	3	RD
4	DTR	6,8	DSR, DCD
6,1	DSR, DCD	20	DTR
7	RTS	5	CTS
8	CTS	4	RTS
5	SGND	7	SGND
9	RI	22	RI

V.35 on DB25 (RS-530-A)

The A and B below refer to each signal pair used in balanced serial interfaces. BEWARE: RS-530 is wired differently. This is the 530-A pinout spec.

Signal/pin primer

Pin No.	Name	Notes/Description
1	Shield	-
2	Transmit Data (A)	-
3	Received Data (A)	-
4	RTS (A)	Request To Send
5	CTS (A)	Clear To Send
6	DCE Ready	Data Communications Equipment Ready (modem/CSU)
7	Signal Common	-
8	DCD (A)	Data Carrier Detect (a.k.a CD or RLSD)
9	Receiver Signal Element Timing (B)	RX Clock
10	DCD (B)	Data Carrier Detect (a.k.a CD or RLSD)
11	Ext Transmit Clock (B)	-
12	Tramsmit Signal Element Timing (B)	TX CLOCK
13	CTS (B)	Clear to Send
14	Transmitted Data (B)	Secondary Transmit Data
15	Transmit Signal element Timing (A)	TX CLOCK
16	Received Data (B)	RX Data
17	Receiver Signal Element Timing (A)	RX CLOCK
18	Local Loopback	-
19	RTS (B)	Request to Send
20	DTE Ready	Host end
21	Remote Loopback	-
22	RI	Ring Indicator
23	Signal Common	-
24	Ext TX Clock (A)	-
25	Test Mode	-

view - looking into male connector

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