Siemens S7-1200 - Page 763

Communication processor and Modbus TCP
12.5 Modbus communication
S7-1200 Programmable controller
System Manual, 03/2014, A5E02486680-AG
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Network 3
This is an optional network that just shows the values of the first 3 words once the
read operation is done.
Network 4
Write 64 bits to the output image register starting at slave address Q2.0.