Applies To:
  • CitectSCADA 1.00 1.01 1.10 1.11 1.20 2.00 2.01 3.00

The Modicon 584 PLC when using the Modbus protocol is very slow to respond to requests for digital addresses (0xxxx & 1xxxx). The cause of this lies in a limitation of the PLC or possibly in the IOP board that interfaces to the PLC.  

To work around this limitation you can use remapped variables to read all digital data up in registers. This will require code changes to the PLC code as the relevant digital bits need to be moved into registers. Testing has shown that this will give up to 800% improvement in performance in reading digital addresses.