Problem with Modbus and Simatic

M

Thread Starter

mareki

I have problem with Modbus communication between Simatic PLCs. In Master PLC I use function blocks P_SND_RK and P_RCV_RK, and I don’t know where I should put slave address. I need specify slave PLC because number of slaves is greater than one.
I have also problem with cable. In documentation there is no information about value of resistance between signal cables (TXD and RXD). Is this resistor necessary.

Best regards
mareki
 
In the Master you have to place the Adress of the slave, the Functioncode and the amount of data (Registers/Coils) with the data in a datablock. Then send this hole datablock to the CP341 or CP441-2 with the Modbus RTU master and then this will work. In the pdf-file off the modbusmaster which is delivered with the driver or may be downloaded from the siemens internet page ("www4.ad.siemens.de/support/index.asp?lang=en":http://www4.ad.siemens.de/support/index.asp?lang=en ). In this pdf-file is everything with examples to read, wenn you buy the driver there is also with the driver a example-project installed.

Best regards
 
I have made everything what is described in this documentation, and I have still problem with Modbus communication between two Simatic PLC's.

Function P_SND_RK is returning error number 1E0F. I can't find this error number in documentation.

Do you have example of project with Modbus communication for Simatic S7??

Best regards
MI
 
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