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I am using freemodbus library for the stm32 modbus TCP client example. But I want to learn how to protech modbus tcp message on the line.
For example Master wants to read 5th holding register from slave, its value 100 but something happenened on the physical line slave send 105 value to Master. This data sends wrong.
How to tell if this message was sent and received correctly. I know there is no CRC-Checksum field in the Modbus frame but is there any way to add it to verify?
I know there is no CRC-Checksum field in the Modbus frame but is there any way to add it to verify?
No, there is no way to add such a field. But Modbus TCP already has a 16 bit CRC and since Modbus TCP sits on on top of TCP it implicitly uses this checksum too.
