Siemens uses Get/Put wizard to complete the analysis of Get/Put Ethernet communication between PLCs

In a system requiring control over multiple stations spread across nearly a kilometer, each station controls one motor to reverse in place. The central control room needs to monitor all the devices connected to the network. With PPI networking between the control units (CNs), the software’s built-in PPI wizard makes configuration very convenient, and the entire network operates using an RS485 interface. However, SMART’s DB9 port does not support PPI communication, but it does support GET/PUT communication via the Ethernet port. This allows for a smooth online GET/PUT communication process. Two SR30 PLCs are used: one as the host (IP address 192.168.2.200) and the other as the slave (IP address 192.168.2.201). The host program is designed to handle the main control logic, while the slave program manages the local operations. The host program includes a visual representation of the logic, showing how data is transferred. Similarly, the slave program also has its own layout, reflecting the specific functions assigned to it. To set up the GET/PUT communication, the wizard is used on the host side. The wizard guides the user through the steps of adding and configuring two PUT/GET operations by default. Each operation can be renamed and commented for clarity. After completing the configuration, the number of operations is displayed. In this case, there are two operations. Configuring the Put function involves mapping the master station’s VB0 to the slave’s QB0, effectively sending one byte of data. For the Get function, the slave’s VB0 is mapped to the master’s QB0, allowing the master to read one byte of data from the slave. Continuing through the wizard, the memory allocation screen shows that the configured data exchange uses 43 bytes of memory on the master PLC (from VB43 to VB85). The next screen displays the components created, including a logic control block, a symbol table, and a data block. The host detects a rising edge on I0.0, which triggers a MOV instruction to set VB0 to 255, meaning all 8 bits of VB0 are set to 1. The configured Put instruction maps this value to the slave’s QB0, causing Q0.0 to Q0.7 on the slave PLC to output. When the falling edge of I0.0 is detected, VB0 is set to 0, and the outputs on the slave PLC stop. Similarly, the slave PLC uses I0.0 to control the host’s QB0, allowing bidirectional control. This setup enables both the host and the slave to control each other’s outputs based on their respective input signals. After downloading the programs, the network is tested. The host PLC (192.168.2.200) is monitored, and the Rx/Tx indicator lights up, confirming the communication link. A screenshot of the host program shows the active logic in action. Next, the sub-station PLC is programmed and connected to the host via an Ethernet cable. When the red button (connected to the host’s I0.0) is pressed, the host detects the rising edge and activates the outputs on the slave PLC. Pressing the green self-reset button (connected to the slave’s I0.0) triggers the slave to send a signal back, activating the host’s outputs. This simple yet effective configuration demonstrates how easy it is to implement GET/PUT communication between two PLCs using the STEP 7-MicroWIN SMART V2.0 environment. It offers a practical solution for remote control and monitoring in distributed systems.

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