By hmimcu 
The controller consists of a program counter, an instruction register, an instruction decoder, a timing generator and an operation controller.
Controllers are divided into combinational logic controllers and microprogram controllers, both of which have their own strengths and weaknesses. Combinational logic controller is troublesome to design and complex in structure, once the design is completed, it cannot be modified or expanded, but it is fast. Microprogrammable controller is easy to design, simple in structure, and easy to modify or expand. To modify the function of a machine instruction, only the corresponding microprogram needs to be reprogrammed.
To add a machine instruction, only a microprogram is added to the control memory, however, it is by executing a microprogram. The comparison is as follows: A combinational logic controller, also known as a hard-wired controller, consists of logic circuits and relies entirely on hardware to implement the function of the instructions.
Extended Information
There are many classifications of controllers, such as LED controller, microprogram controller, access control controller, electric car controller, bus controller, automatic transfer switch controller, single chip microcontroller, etc.
1, controller (LED controller): through the chip processing control LED lights circuit in each position of the switch. Controller according to the pre-set program and then control the driver circuit to make the LED array regularly light, so as to display the text or graphics.
2, micro-programmable controller: micro-programmable controller compared with the combined logic controller, has a series of advantages such as regularity, flexibility, maintainability, etc., and therefore in the computer design gradually replaced the early use of combined logic controller, and has been widely used. In the computer system, microprogramming technology is the use of software methods to design the hardware of a technology.
3, access control: also known as access management control system (Access Control System), which is based on the development of the traditional door lock. Access controller is the core of the system, the use of modern computer technology and the combination of various identification technologies, reflecting – an intelligent management means.
4, electric car controller: electric car controller is used to control the electric car motor start, run, in and out, speed, stop and other electronic devices of the electric car core control device, it is like the brain of the electric car, is an important part of the electric car.