Siemens SIMATIC S7 CP340 Programming Manual page 53

5 MODBUS RTU Protocol communication
Fig. 94: Open Modbus Slave test software
2. Click the button Register Later. This software may be used for 30 days without
registration, but each time it may only be used for 15min. The software downloaded
from the Internet has no registration code. Then click the menu Connection-
>connect to configure the serial parameters, which shall be the same as the CP341
parameters.
Fig. 95: Setting communication parameters
3. Click OK, and then select the menu Setup->Slave Definition... to set the
communication data. As CP341 uses function code 3,03 Holding Register shall be
used. The address of the slave accessed by CP341 is 2, and Slave ID is set as 2.
The start address starts from 1. See the screen below:
CP340/CP341/CP440/CP441 Communication and Programming
Entry-ID: 88867653, V1.0, 02/2014
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