In the previous discussion, to design a micro programmed control unit, we have to do the following:

• For each instruction of the CPU, we have to write a microprogram to generate the control signal. The microprograms are stored in microprogram memory (control store). The starting address of each microprogram are known to the designer


• Each microprogram is the sequence of microintructions. And these microinstructions are executed in sequence. The execution sequence is maintained by microprogram counter.


• Each microinstructions are nothing but the combination of 0’s and 1’s which is known as control word. Each position of control word specifies a particular control signal. 0 on the control word means that a low signal value is generated for that control signal at that particular instant of time, similarly 1 indicates a high signal.


• Since each machine instruction is executed by a corresponding micro routine, it follows that a starting address for the micro routine must be specified as a function of the contents of the instruction register (IR).


• To incorporate the branching instruction, i.e., the branching within the microprogram, a branch address generator unit must be included. Both unconditional and conditional branching can be achieved with the help of microprogram. To incorporate the conditional branching instruction, it is required to check the contents of condition code and status flag.