Microprogram controller definition
A controller that uses microprogram control is called a microprogram controller. The so-called micro-program control mode means that the micro-command is not generated by the combinational logic circuit, but is generated by the micro-instruction decoding. A machine instruction is often executed in several steps. The number of bits required for each step of operation is written in code form in a microinstruction. A number of microinstructions form a microprogram corresponding to a machine instruction. When designing the CPU, each segment of the microprogram is prepared in advance according to the needs of the command system, and they are stored in a dedicated memory (called control memory). The microprogram controller is composed of an instruction register IR, a program counter PC, a program status word register PSW, a timing system, a control memory CM, a microinstruction register, a micro address forming circuit, a micro address register, and the like. When executing the instruction, the corresponding micro-program segment is found from the control memory, the micro-instruction is fetched one by one, and the micro-instruction register is sent, and the required micro-command is generated after decoding, and the operation of each step is controlled.