Point-to-point link
Communication
Function Manual, 12/2017, A5E03735815-AF
125
Procedure for setting up Modbus communication (RTU)
1. Configure an S7-1500 configuration with CPU and CM in the device view of the hardware
and network editor of STEP 7.
2. In the Project tree, select the "Program blocks" folder and open OB1 in the folder by
double-clicking on it. The program editor opens.
3. Select the instructions for Modbus communication according to your task in the
"Communication" area, "Communications processor" folder of the "Instructions" task card
and drag them to a network of OB1:
– The "Modbus_Comm_Load" instruction configures the port of the CM for Modbus
communication.
– The "Modbus_Master" instruction is used for Modbus master functionality.
– The "Modbus_Slave" instruction is used for Modbus slave functionality.
4. Assign the parameters for the instructions according to your configuration.
5. Download the hardware configuration and user program to the CPU.
● You can find more detailed information on communication via point-to-point connections
and basics of serial data transmission in the function manual CM PtP communication
module - Configurations for point-to-point connections
(http://support.automation.siemens.com/WW/view/en/59057093
).
● You can find a description of how to use the instructions for point-to-point connections in
the user program in the STEP 7 online help.
● You can find information about the communications modules with a serial interface in the
manual of the particular communications module.
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