Communications Setup
372 SPU 780 01EMAN May 2002 67
Configuring Modbus Communications
Overview Modicon’s master/slave protocol, standard on 984 and many other controllers.
Select this option if your computer is connected to a controller’s Modbus port, either
directly or through a modem.
Setting Modbus
Parameters Select the Modbus tab and set the following communications parameters:
When you have finished configuring the parameters, press OK.
Note: The controller must have the same Modbus settings as the computer. Set
Modbus parameters for your PLC with the Ports tab of the Controller Configuration
window or with its DIP switches.
Parameter Description
Modbus Address The Modbus address of the PLC.
Port Identifies which serial port on your PC is connected to the controller
or modem (if you are connecting to the controller through one).
Default is COM1.
Baud Rate Sets the data transfer speed of your PC’s serial port in bits per
second. The PC and controller must be set to the same baud.
Default is 9600.
Parity Adds a check bit to a packet to make the number of binary ones
always either odd (Odd parity) or even (Even parity). If parity is set
to None, the check bit is not added. The PC and controller must use
the same parity. Default is Even.
Stop Bits Sets the number of bits at the end of a packet prepares the
receiving device for the next packet. The PC and controller must
use the same number of stop bits. Default is 1.
Data Mode Identifies which data protocol (Remote Terminal Unit or ASCII) to
use. Both the PC and controller must use the same data protocol.
Default is RTU.
Timeout Specifies the length of time the PC will wait for successful
communication with a controller before displaying an error
message. Default is 3 seconds.
Modem Type If your computer is connected directly to the controller, set the
Modem Type to None. If your computer is directed to the controller
through a modem it must be configured. See Modbus
Communications by Modem.