Modbus Rtu Master Example Program - Siemens SIMATIC S7 System Manual

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Modbus RTU master example program

MB_COMM_LOAD is initialized during start-up by using the first scan flag. Execution of

MB_COMM_LOAD in this manner should only be done when the serial port configuration will

not change at runtime.

Network 1 Initialize the RS-485 module parameters only once during the first scan.

One MB_MASTER instruction is used in the program cycle OB to communicate with a single

slave. Additional MB_MASTER instructions can be used in the program cycle OB to

communicate with other slaves, or one MB_MASTER FB could be re-used to communicate

with additional slaves.

Network 2 Read 100 words from the slave holding register.

S7-1200 Programmable controller

System Manual, 11/2011, A5E02486680-05

105BCommunication processor

12.5 Modbus communication

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Simatic s7-1200