TCP Modbus + nModbus

[Wisse]

Hi there

I'm working on a project for UNI. My basic goal is to read data off Ethernet enabled Vision V130 via Modbus, using C# nModbus library.

PLC is configured, following example from VisiLogic help, to act as TPC Modbus slave, while custom software on PC. acting like Modbus master, takes care of data reading. I managed to get everything working. I could see coil states and 16/32-bit register values on my PC. So far so good. Problems started when I upgraded VisiLogic to the latest version (8.6.1) and with it, PLC's O/S. From that point on, I couldn't read anything anymore. Debug showed "null" as read value. My best guess is that something has changed in PLC's Modbus message structure, which made it incompatible with nModbus. Both, PLC and PC programs stayed the same.

I read change logs and noticed few changes regarding Modbus, but I can't tell if that's the cause. That's why I'm turning on you for help.

Thanks, Wisse.

Old (working) version:

VisiLogic 8.0.1 Build 0, PLC: V130-33-R2(A), O/S: 3.0(09), Boot: 2.1(01), Factory boot: 1.1(00)

New (not working for me) version:

VisiLogic 8.6.1 Build 0, PLC: V130-33-R2(A), O/S: 3.1(19), Boot: 2.2(02), Factory boot: 1.1(00)