Chapter 2: Modbus PLCs Using Modbus
17
584 Military Connector
25-Pin Modems (J478)
For applications requiring additional Modbus ports, it is recommended that Modbus expanders be
used. Modbus Port Expanders from Modicon may be used to connect multiple Operator Stations to a
single PLC. The Operator Station communications cable previously described may be used to connect
the Operator Station and the PLCs to a Modbus Port Expander.
Communications Parameters
For each Modicon port used, certain parameters must be set in order to establish communications with
the Operator Station. This is accomplished either through dipswitch settings on the individual module
or programming selections using the Modicon P230 Programmer.
Standard communication parameters for communicating with Modicon PLCs using Modbus are:
7 data bits for ASCII mode and 8 data bits for RTU mode
1
stop
bit*
9600
baud
rate
ASCII or RTU mode**
No
parity
*2 stop bits for 984-38X, 984-48X, 984-68X
**Depending on the driver selected in the PLC Name and Port Table, you must select either ASCII or
RTU mode to communicate to an Operator Station. All other parameters should be configured as
listed above.
Note:
The following is a summary of the information available at the time of this manual’s printing,
describing the necessary settings for each PLC model. Be sure to check with Modicon for
any possible updates or changes if you encounter any difficulty.
