Modbus Master for CP340/CP440


Thread Starter

Andre Janssens

I need to communicate with a black box wich can communicate with Modbus. My PLC is a S7-300 series and a CP340 communication card.
I have an example for Modbus Slave RTU but not for Modbus Master RTU. Who can provide me with a Modbus Master RTU protocol for Siemens S7-300/S7-400?
Thanks in forehand!
I think you have the wrong CP card.
The one for you is , in my opinion, CP341. It is more expensive, but it is possible to load on it the modbus protocol (RTU & ASCII, Master & Slave). The advantage is that you have just to load the protocol you need (provided By Siemens too) without implementing it by yourself.
Unfortunately you have to pay for both the CP and the protocol you need.

Andre Janssens

Thank you Antonio,
I thought so. So I bought (!) the Modbus Master and Slave RTU protocol from Siemens and use now CP341 and CP441-2. And it works perfectly.