To get ready for a startup, I am creating a slave and master with two S7-1200s. I finished programming both PLCs, butthe masterdoes not work.
Objective: The master is reading from the slave holding register.
Troubleshooting: I'm pretty sure the logic is correct. I used a computer with modbus scan to read from the slave holding register. I got the data that I expected usingthe computer. I could see the data with the computer. When I looked at the data, it included the data + 16 bitsof the CRC checksum.
Then I looked at the master. The master is sending the following data:
020300000001 + 8 bits of the CRC checksum. 16 bits address, 16 bits function code, 32 bits for address and length. The problem is that the chechsum is only 8 bits. My slave is expecting 16 of checksum.
The checksum is being truncated. I checked what the checksum should be and the 8 bits are correct except that it is missing the other 8 bits.
Does anyone know why my checksum is being truncated?
Thanks in Advance, Victor

Problem solved.

I did do all the software updates.I think part of the problem was my fault 'cause I useda modbus scanner to monitor the traffic andthe software wasn't showingall the traffic and that added to my confussion.

Thanks for your help,

Victor