Applies To:
  • CitectSCADA 5.20

I need to be able to read and write to General Reference Registers (Extended Memory) using the Citect Modbus or Modnet drivers. Is this possible? 

The Modnet, Modbus , ModbusA and Mbplus drivers now provide the capability to Read and Write General Reference Registers (Modbus protocol commands 20 and 21).

Tag addressing to facilitate reading and writing these registers is as follows: The syntax for the new extended registers is: Ef:r where f is the file number in the range of 1 to 999 and r is the register number in the range of 0 to 9999 OR Ef:r.b where b is the bit to access which can range from 1 to 16.

Extended Memory Registers are often referenced in the 6XXXXX format. ie the very first register is 600000 then 600001 etc (note that this is different from the Holding registers where the first register is actually 40001 not 40000).

600000 is equivilent to E1:00000
600001 is equivilent to E1:00001