Applies To:
  • CitectSCADA 6.xx, 7.xx

Some PLC/controller has different specifications on which variable type they will/can reply on during the communication initialization to Citect through the Modbus Driver.

For example, OMRON Sysdrive 3g3mv can only replies to command type 3, 8, and 10. By default, modbus protocol will try to read variable type 2 on startup for initialization and it will not be replied by OMRON Sysdrive.

Therefore, we need to change the initialization type on modbus protocol to cater the need to communicate with the PLC succesfully.

There is an simple way to do it by just altering the [MODBUS] InitType parameter according to what variable type the PLC can reply. Taking the example above, we can add up Citect.ini file with the following parameter:

[MODBUS] InitType = 3

In that case, modbus protocol will try to read variable type 3 on startup and it will be replied by the PLC.

modbus, InitType, initialization, OMRON, parameter, modnet, startup, variable type.