Festo Modbus and FANUC Robot's TCP/IP

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Heya all, 

I was wondering if anyone of you have every configured the FESTO Modbus device or controller with FANUC robot (anyone)? Once working with a group, they configured the FESTO device with FANUC but Festo device was not seeing any kind of I/O data from the robot.

Both of the devices were un-faulted too and were seem to have communicated well. I was curious if there is any kind of offset in the data or what can be the possible reason? Any words of wisdom would make my day.

Thank you