Controller (English name: controller) refers to a master device that changes the wiring of the main circuit or control circuit and changes the resistance value in the circuit according to a predetermined sequence to control the start, speed, brake and reverse of the motor. It is composed of a program counter, instruction register, instruction decoder, timing generator and operation controller. It is the "decision-making body" that issues orders, that is, it coordinates and directs the operation of the entire computer system.
Controllers are divided into combinational logic controllers and microprogram controllers. Both controllers have their strengths and weaknesses. The design of the combinational logic controller is troublesome and the structure is complicated. Once the design is completed, it cannot be modified or expanded, but it is fast. The microprogram controller is easy to design, simple in structure, and easy to modify or expand. To modify the function of a machine instruction, you only need to reprogram the corresponding microprogram; to add a machine instruction, you only need to add a microprogram in the control memory. However, it is done by executing a micro process. The specific comparison is as follows: The combinational logic controller, also known as the hard-wired controller, is composed of logic circuits and completely relies on hardware to realize the function of instructions.