How Does PLC Communicate with HMI? [Essential Knowledge]

When we are establishing communication between HMI and PLC, we need to address a key issue, which is the parameter settings for the communication connection between HMI and PLC. This is a common question among many learners and is a focal point of our study. The communication between the touchscreen and PLC can be divided into several types: one is when the HMI controls a local PLC; the other is when the HMI controls a remote PLC. Let’s first learn how to control a local PLC using the Weinview Touchscreen, specifically how to set its parameters.

First, we need to understand what is meant by “local PLC”?

The term “local PLC” refers to the PLC that is directly connected to the local HMI. If we want to control the local PLC, we need to add this type of device first. The operation method is as follows:

1. Click on the “Edit” menu and select “System Parameter Settings”. In the pop-up dialog, click “Add” to open the “Device Properties” dialog.

2. In the opened “Device Properties”, set the parameters for the local PLC. We need to set the device name, location, PLC type, interface type, etc. Here, we will set the PLC type to MODBUS RTU as an example, as shown in the figure below.

It is important to note that the PLC interface type can be selected as RS-232, RS-485 2W, RS-485 4W, Ethernet, USB, or CAN Bus. If the interface type is RS-232, RS-485 2W, or RS-485 4W, you can click on “Settings” in the dialog box to open the “Communication Port Settings” dialog, where you can set the communication port parameters, including communication port, baud rate, data bits, parity, stop bits, etc.

If the interface type is Ethernet, you can click on “Settings” in the dialog box to open the “IP Address Settings” dialog, where we need to correctly set the PLC’s IP address and port number. If we select the PLC type as S7-200 Smart Ethernet, the interface type is set to Ethernet by default.

If the interface type is USB, no further settings are required, just check that the values in “Device Properties” are correct. After completing the above settings, you will find a new device named “Local PLC 1” in the device list, thus completing the parameter settings required for the touchscreen to control a local PLC.

These are the key points for setting parameters for controlling a local PLC using the Weinview touchscreen. Did everyone get it?

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