Applies To:
  • CitectSCADA 3.xx, 4.xx, 5.xx, 5.20
Summary:
I'm trying to get Citect to talk to an Ingersol Rand Compressor, which has a Universal Communication Module (UCM). The UCM can communicate via Modbus to Citect, but it only lets Citect read 16 Modbus Registers (either bits or words) in the one block read request. The Modbus protocol is configured to read 32 Modbus registers in the one request. What needs to be modified to allow Citect to talk to this device via Modbus? 

Solution:
You will have to change the MaxLength parameter in the ProtDir.DBF for the Modbus protocol and the MaxBits parameter in the Citect.INI file for the Modbus protocol. The default for both of these is 2000. Reset both of these to 256 (this number must be devisable by 16).

Then change the BitBlock Parameter in the ProtDir.DBF for the protocol and in the Citect.INI file for the protocol. The default is 400, change both to 48 (this number must be devisable by 16).

You also have to make sure that the BitBlock parameter is lower than the MaxLength parameter. Then change the Block parameter in the Citect.INI file for the Modbus protocol to 5.

Restart Citect, pack, recompile, then test out your communications.

 
Keywords:
 

Attachments