In hardwired control, we saw how all the control signals required inside the CPU can be generated using a state counter and a PLA circuit.
There is an alternative approach by which the control signals required inside the CPU can be generated . This alternative approach is known as microprogrammed control unit.
In microprogrammed control unit, the logic of the control unit is specified by a microprogram.
A microprogram consists of a sequence of instructions in a microprogramming language. These are instructions that specify microoperations.
A microprogrammed control unit is a relatively simple logic circuit that is capable of (1) sequencing through microinstructions and (2) generating control signals to execute each microinstruction.
The concept of microprogram is similar to computer program. In computer program the complete instructions of the program is stored in main memory and during execution it fetches the instructions from main memory one after another. The sequence of instruction fetch is controlled by program counter (PC) .
PC).