How does the touch screen control the PLC?

The control of PLC itself is achieved by changing state variables such as control register D, input port X, soft relay status M, and time relay T. Therefore, as long as the status of these variables can be modified, control of PLC can be completed. The touch screen can complete these operations through communication with PLC's 232 or 485 ports, so the touch screen can control PLC.

Monochrome Tft

The touch screen can be understood as a "soft dashboard and button panel". The buttons on the touch screen actually work on the same principle as buttons in reality, which are in two states of switch. They both have an address, and the actual button may be I0.0, while the touch screen button may be M0.0. This type of compliance represents a switch variable of two states, and the actual button is directly input into the PLC through an external port, The essence is to determine a fixed address, and the touch screen is the same. The determined address is the same as the PLC, and it directly modifies the status inside.

Many times, PLC manufacturers do not open these addresses and variables on the communication port, but there is a program editing and downloading window between the PLC and the computer. It is said that touch screen manufacturers have cracked this window and mastered its communication format, so they can directly communicate and modify the PLC status.