The PLC itself is controlled by changing the state variables such as control register D, input port X, soft relay state M, and time relay T, so as long as the state of these variables can be modified, the control of the PLC can be completed. However, the touch screen layers can complete these operations through the communication of the 232 or 485 port of the PLC, so the touch screen layers can control the PLC.
The touch screen layers can be understood as a "soft dashboard and button panel". The buttons on the touch screen actually work the same as the buttons in reality. They are two states of on/off. They all have an address. The actual button may be I0.0.
The button of the touch screen layers may be M0.0. Such a conformity represents a two-state switch variable. The actual button is directly input to the PLC through the external port. The essence is to determine a fixed address, and the touch screen layers are the same. The determined address is the same as that of PLC, and the state in it is directly modified.
In much of the time, PLC manufacturers do not open these addresses and variables in the communication port, but there is a program edit and download window between the PLC and the computer, indicating that the touch screen manufacturer has cracked this window and mastered its communication format, so it can directly communicate to modify the PLC status .
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