Note: This Calculation is not valid for Communication with optional communication interface card CI532V02 (AC110/410/450) witch uses DAT-database elements instead of PD-database elements.

To calculate the Modbus digital address use the formula (1):

N * 32 - (M - 1)            (1)

For example: If you have a PLC digital address, PD4:7. Then N = 4, and M = 7. This equals to 122. Now you have to add the Modbus prefix at the beginning off the address, 00 to read and write from Citect, 10 for reading only. The Modbus address for PD4:7 corresponds to 00122 (for read and write). Integers are calculated in much the same way.

To calculate the Modbus word address use the formula (2):

(N * 2) - 1                 (2)

For example: If you have a PLC word address PD (I) 106. Then N = 106. This equals to 211. In this case you have to add the prefix 40, so the address for PD (I) 106 equals to 40211.

For best communication results, try setting the Modbus Citect.ini parameter to the following:

[Modbus]
Block = 15
Delay = 300
InitType = 1
TimeOut = 500
MaxBits = 512

The MODBUS driver allows reading of 2000 bits in one request. The ABB Advant does not support such large reads. You can change the maximum read size with the [MODBUS] MaxBits parameter. You must also change the MAX_LENGTH field for the MODBUS protocol (in the \CITECT\BIN\PROTDIR.DBF file) to the same value.

The default port parameters on the PLC port are 9600, N, 8, 1.  Citect must be adjusted to fit these parameters.