Building Null-Modem Cables (Rs-232); Building Null-Modem Cables (Rs-422); Building Straight-Through Cables (Rs-232/485) - Comtrol DEVICE MASTER RTS Hardware Installation And Configuration

Building Null-
Modem Cables
(RS-232)
Building Null-
Modem Cables
(RS-422)
Building Straight-
Through Cables
(RS-232/485)
Connecting Serial Devices
Use the following figure if you need to build an RS-232 null-modem cable. A null-
modem cable is required for connecting DTE devices.
DB9
Signal
Pins
TxD 3
RxD 2
RTS 7
CTS 8
DSR 6
DCD 1
DTR
4
GND 5
RI
9
Note: You may want to purchase or build a straight-through cable and purchase a
null-modem adapter.
Use the following figure if you need to build an RS-422 null-modem cable. A null-
modem cable is required for connecting DTE devices.
Note: RS-422 pinouts are not standardized. Each peripheral manufacturer uses
different pinouts. Please refer to the documentation for the peripheral to
determine the pinouts for the signals above.
Use the following figure if you need to build an RS232 or RS-485 straight-through
cable. Straight-through cables are used to connect modems and other DCE
devices.
Signal
DCD
RxD
TxD or TRx-
DTR
GND
DSR
RTS or TRx+
CTS
RI
RJ45
DB9
Pins
Pins
4
5
1
8
7
6
2
3
N/A
DB9 RJ45 RJ45
Signal
Pins Pins Pins
TxD+ 7 1
TxD- 3 4
RxD+ 8 8
RxD- 2 5
DB9 RJ45 DB9
Pins Pins
Pins
1 6
2 5
3
4
4
2
5 3
6
7
7
1
8 8
9
N/A 9

Building Null-Modem Cables (RS-232)

DB25
RJ45
Pins Pins Signal
2 RxD
3
5
3 TxD
2
4
CTS
8 5
8
RTS
7
4 1
DTR
4
20 2
DCD
1
8 6
DSR
6
6 7
GND
5
7
3
9 RI
22 N/A
Signal
RxD+
RxD-
TxD+
TxD-
RJ45
DB25
Pins
Pins Signal
1 6 8
DCD
2 5 3
RxD
3 4
2
TxD or TRx-
4 2
20
DTR
3
5 7
GND
6 7
6
DSR
7 1
4
RTS or TRx+
8
8 5
CTS
N/A
22 RI
15