Modbus TCP and Modbus RTU

CODESYS
1

Hi, I have a network with 5 remote I/O modules Modbus TCP(750-362), all controlled by a single master (PFC200). In addition, I have 5 other devices that can only be accessed via Modbus RTU remotely, as well as some devices located locally next to the PLC.

I trying to determine the best approach to establish communication between the master and all devices.
I can already reach all the remote I/O modules through Modbus TCP. I was considering attaching a 750-652 (RS485) module to the remote I/O stations in order to communicate with the RS485 devices remotely and use the remote I/O as a converter for the RS485 devices.

For the local RS485 devices, I am considering either using another 750-652 or the RS485 port built-in the PLC. My goal is to be able to access all remote devices via Modbus TCP, and communicate with local devices either through 750-652 module or the PLC’s RS485 port.

If you have any recommendations or alternative approaches, I would really appreciate your advice.

Thanks

2

Hi William,

It sounds like some of your RS485 devices are not necessarily Modbus RTU. In that case, it makes sense to me that you isolate those devices on another network from the Modbus devices. I would probably use the built in 232/485 port for Modbus RTU devices and the 750-1657 module for the other serial devices. (1657 is the newest serial module). The ModbusTCP devices are obviously on Ethernet, you can either use the configuration option in Codesys for those devices, or use the WagoAppPlcModbus library and use a fbModbusMasterTCP.

3

Hello. This is Matthew Kim from Korea.

It seems the model name above is incorrect.

The 750-1657 is an IO-LINK module.

It appears there was a typo while trying to recommend the 750-1652 product.

4

Hi Mike,

Thanks for your response. Now, I found a TCP card that is connected to my drive (for controlling the motor speed), so all devices will communicate over ModbusTCP. My setup is a PFC200 as the master, an ethernet switch, and all slave devices connected through it. Do you happen to have any example code for Modbus TCP?

Anything you could share would be really helpful.

Thanks