The controller is composed of a program counter, an instruction register, an instruction decoder, a timing generator, and an operation controller. Its main functions are:
(1) Fetch an instruction from memory and indicate the location of the next instruction in memory.
(2) Decode and test the instructions, and generate corresponding operation control signals to facilitate the execution of specified actions.
(3) Directs and controls the direction of data flow between CPU, memory, and input and output devices.
In the microprocessor, the ALU, the counter, the register and the control part are interconnected through the internal bus, and connected with the external memory and the input and output interface circuit through the external bus. The external bus, also known as the system bus, is divided into a data bus DB, an address bus AB and a control bus CB. Through the input and output interface circuit, the connection with various peripheral devices is realized.
