I have a problem with modbus communication between TSX Premium PLC (modbus module in rack TSX SCY 21601) and TCI-c card for TRANE RTAC 200 chiller.

The TCI-c card doesn't reply on question READ_VAR(...) and WRITE_VAR(...). It means I can't write and read data from the chillers.

Does anyone know this problem and could help me to solve it?

 

I think that you need first test the communication port of chiller with other device diferent of a PLC. you can use a Modbus OPC server demo. you can get this demo from http://www.kepware.com or software toolbox, these softwares are installed in a PC with windows 2000 or XP. you only need one serial port in your PC or a rs232 to rs485 convert if is necesary.

the opc server come with a tool to test modbus protocol and you can read and write data in the registers.

too, maybe crane modbus interface is wrong configurate any you need crane support to re-configurate this module.

I think that crane support have a software tool to test chiller modbus interface. and you will be sure that don't has a problem with this device.