i would like to establish communication between S7-300 and communication module cp340- rs232  so that i can use it as  modbus to connect with pm240 inverters .i have cpu 314c-2dp model . please tell me how .

RC23

Check the link below. There is a pdf doc under documentation. That might help!

http://plc.myforum.ro/modbus-tcp-communication-of-pcs-7-with-third-party-systems-vt4224.html

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Split from Modbus / TCP communication with STEP 7 V5.5.

Hello m. tahboub;

With a S7-300 CPU  and a serial CP (RS-232 in our case) you can setup Modbus RTU connexions; is that what you need to do?

The Modbus RTU master (or slave) for a S7-300, as developped by Siemens, requires a CP 341, with a loadable driver for Modbus RTU and a physical dongle inserted in he CP module. You could not do it with a CP 340.

However, member Tibi68 has proposed a solution for the CP 340, which you can download here:

MODBUS RTU MASTER FOR CP340/341/441-X (NO DONGLE REQUIRED)

You do not require the Siemens Modbus driver for this; on the other hand, you will get no support from Siemens,only from Tibi68 directly, through the link above.

Hope this helps,

Daniel Chartier

Hello,

or you can also implement your own communication, in case of only one request with no changed requirements, it can be solved also. Of course, good experience in serial communication and Modbus is important. One very important thing, you have RS-232 module so only one inverter you can connect to this module, also distance of cable is very limited due RS-232 specification.