Help on Siemens PLC

Hi Dear Friends,

I have to get data from a third party device into the Siemens S7 300 PLC. Now the protocol the third party device supports is Modbus RTU protocol and the PLC has a communication processor (CP 340) which supports Modbus ASCII protocol.

I am confused how to go about it. I saw a live machine working using such a method of communication. How is this possible? How can be this Modbus RTU converted into Modbus ASCII? Any ideas?

Thanks,
Sudheendra

Hi!
You will have to write your own FBs to achieve the RTU variant.

But

I mean to recall that there was a member of the forum that had made FBs for Modbus RTU master and slave to be used on CP340 (not very expensive). I tried to search but couldn't find the thread. I think it must have been less than 2 years since.
Any of you others that have a clue?

Kalle

Edit: I found the post http://www.plctalk.net/qanda/showpost.php?p=395759&postcount=7
ByteSlicer has the address www.runmode.com

The CP341 supports modbus RTU (Master and Slave), you have to buy a license from siemens for the FB library.

An alternate would be to use the Et200s expansion (if your CPU has a profibus port) and use the Serial interface module. The FB library is free for this module.

Thanks Kalle.. it was helpful