Hardware reference guide
CPU Modules
172
35013379 02 October 2007
Modbus Ports 
Pinout 
Connections
The following figure shows the Modbus port pinout connections for 9-pin and 25-pin 
connections. 
5
IBM-AT
9-Pin Female
Quantum
9-Pin Male
Quantum
9-Pin Male
IBM-XT
25-Pin Female
CD 
RX
TX 
DTR
GRND 
DSR
RTS 
CTS
1
2
3
4
5
6
7
8
1
2
3
4
6
7
8
9
SHIELD 
RX
TX 
DTR
GRND 5
DSR
RTS 
CTS
NC
1
2
3
4
6
7
8
9
SHIELD 
RX
TX 
DTR
GRND 
DSR
RTS 
CTS
NC
RX
RTS
CTS 
DSR
GRND
NC
1
2
3
4
5
6
7
8
SHIELD 
TX 
20DTR
This document provided by Barr-Thorp Electric Co., Inc. 800-473-9123 www.barr-thorp.com










