The control unit can generate the control signals for any instruction by sequencially reading the CWs of the corresponding microprogram from the microprogram memory. To read the control word sequentially from the microprogram memory a microprogram counter (PC) is needed.

The basic organization of a microprogrammed control unit is shown in the Figure 5.17.

The "starting address generator" block is responsible for loading the starting address of the microprogram into the PC everytime a new instruction is loaded in the IR.

The PC is then automatically incremented by the clock, and it reads the successive microinstruction from memory.