PLC adopts the "sequential scanning, continuous circulation" working mode
1. Every scan process. Focus on sampling the input signal. Focus on refreshing the output signal.
2. Enter the refresh process. When the input port is closed, when the program is in the execution phase, the input has a new state and the new state cannot be read. The new state is only read when the program performs the next scan.
3. A scan cycle is divided into input samples, program execution, and output refresh.
4. The contents of the component map registers vary as the execution of the program changes.
5. The length of the scan cycle is determined by three bars. (1) The speed at which the CPU executes the command (2) The time the command itself occupies (3) The number of instructions.
6. Due to the use of centralized sampling. The way to concentrate output. There is a phenomenon of input/output hysteresis, that is, input/output response delay.