User guide

Communication Capabiliites
70
890 USE 108 00 August 2001
Modbus Communications A984 & E984-241/251
9-Pin Port/Cable
Pin-Outs
The A984-1xx and E984-241/251 CPUs are equipped with a nine-pin RS-232C
connector that supports Modicon’s proprietary Modbus communication protocol.
For connection to a 25-pin XT-type panel, use a Modicon W951 (null modem)
cable or the cable shown in the figure that follows.
For connection to a 9-pin AT-type panel, use a Modicon AS-W952-01 2 cable.
The W952 cable is 12 ft long.
The following figure shows the Modbus port pinouts (Controller to 9-Pin and 25-
Pin Panel Connections)
Modbus Protocol
Features
The Modbus protocol can be used for programming or for data transfer; the
controller responds to transactions initiated by a host device connected to the
controller’s communication processor at a Modbus port. Modbus facilitates
communication with host devices, such as a programming panel or a P965 Data
Access Panel, and it also supports a multi-controller (master-slave) communications
networking strategy. The P965 does not support the E984-258/265/275/285 PLCs.
6
IBM-AT
9-Pin Female
Quantum
9-Pin Male
Quantum
9-Pin Male
IBM-XT
25-Pin Female
CD
RX
TX
DTR
GROUND
DSR
RTS
CTS
1
2
3
4
5
6
7
8
1
2
3
4
6
7
8
9
SHIELD
RX
TX
DTR
GROUND
5
DSR
RTS
CTS
NC
1
2
3
4
7
8
9
SHIELD
RX
TX
DTR
GROUND
5
DSR
RTS
CTS
NC
RX
RTS
CTS
DSR
GROUND
NC
1
2
3
4
5
6
7
8
SHIELD
TX
20DTR