Siemens SIMATIC ET 200AL, System Manual

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Communication
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Function Manual, 05/2021, A5E03735815-AJ
Procedure for setting up USS communication
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 USS 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 "USS_Port_Scan" instruction allows you to communicate via the USS network.
– The "USS_Drive_Control" instruction prepares send data for the drive and evaluates the
response data of the drive.
– The "USS_Read_Param" instruction is used to read out parameters from the drive.
– The "USS_Write_Param" instruction is used to change parameters on the drive.
4. Assign the parameters for the instructions according to your configuration.
5. Download the hardware configuration and user program to the CPU.
Properties of the Modbus protocol (RTU)
• Communication takes the form of serial, asynchronous transfer with a transmission speed
of up to 115.2 kbps, half duplex.
• Data transfer works according to the master-slave principle.
• The Modbus master can send jobs for reading and writing operands to the Modbus slave:
– Reading inputs, timers, counters, outputs, memory bits, data blocks
– Writing outputs, memory bits, data blocks
• Broadcast to all slaves is possible.
Data exchange using Modbus communication (RTU)
The communications module can be a Modbus master or Modbus slave. A Modbus master
can communicate with one or more Modbus slaves (the number depends on the physical
interface). Only the Modbus slave explicitly addressed by the Modbus master is permitted to
return data to the Modbus master. The slave detects the end of the data transfer and
acknowledges it. If an error occurs, it provides an error code to the master.