Working mode
PLC:
PLC adopts a cyclic scanning working mode. It is like a staff member who follows the routine, strictly following the fixed order of input sampling, program execution, and output refresh. In a scanning cycle, it will first collect and store the status of all input signals, then execute the program written by the user, and finally output the results after the program execution. This working mode makes the program execution deterministic and predictable, and is suitable for handling sequential control and logical control tasks in industrial control.
MCU:
The working mode of the MCU is relatively flexible. It can use the method of sequential execution of programs, just like PLC to execute the code in sequence, but it can also use the interrupt-driven method. The interrupt is like an “emergency channel”. When an external interrupt signal (such as an emergency request from an external device) arrives, the MCU can suspend the executing program and deal with the emergency instead. After the emergency is dealt with, it will come back to continue to execute the original program. This working mode enables the MCU to respond quickly to some sudden external events, which is suitable for application scenarios with high real-time requirements.
Program execution order
PLC:
Because PLC works in a cyclic scanning cycle, the program execution order is fixed. In each scanning cycle, input sampling is performed first, then the program is executed, and finally the output is refreshed. This sequential execution is conducive to stable control of complex industrial processes because it ensures that the way of processing input and output is consistent each time.
Microcontroller:
Microcontrollers execute programs sequentially without interruptions, but when an interrupt occurs, the execution order will be interrupted. For example, a microcontroller is executing a data acquisition program, and suddenly an external interrupt signal indicates that there is urgent data to be processed. The microcontroller will pause the data acquisition program to process the urgent data, and then return to the interrupt point of the data acquisition program to continue execution after processing. This flexibility makes the microcontroller more advantageous in some occasions where rapid response to external changes is required.
Application scenario focus
PLC:
PLC is mainly used in the field of industrial automation control, such as factory production line control, elevator control, chemical process control, etc. It focuses on processing a large number of input and output signals, and there are often complex logical relationships between these signals, such as interlocking control and sequential control. For example, on an automobile production line, a PLC can control a series of operations such as the welding sequence of a robot and the start and stop of a conveyor belt.
Single-chip microcomputer:
The application scenarios of single-chip microcomputers are more extensive. In addition to industrial control, they are also widely used in consumer electronics, smart homes, IoT devices and other fields. It focuses more on controlling a single device or a small system, and performs well in situations where real-time events need to be processed quickly or are cost-sensitive. For example, in a smart bracelet, a single-chip microcomputer can be used to process sensor data, control display screens, and communicate with mobile phones via Bluetooth.
