Design of Control Unit

Control unit generates timing and control signals for the operations of the computer. The control unit communicates with ALU and main memory. It also controls the transmission between processor, memory and the various peripherals. It also instructs the ALU which operation has to be performed on data.

Control unit can be designed by two methods which are given below:

Hardwired Control Unit

It is implemented with the help of gates, flip flops, decoders etc. in the hardware. The inputs to control unit are the instruction register, flags, timing signals etc. This organization can be very complicated if we have to make the control unit large.

If the design has to be modified or changed, all the combinational circuits have to be modified which is a very difficult task.

Micro programmed Control Unit

It is implemented by using programming approach. A sequence of micro operations is carried out by executing a program consisting of micro-instructions. In this organization any modifications or changes can be done by updating the micro program in the control memory by the programmer.

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