Control Unit

The control unit is the part of a digital system that controls and sequences the datapath's operations. The control unit is an example of a sequential logic circuit and it is easy to find examples both of Moore and Mealy models. The inputs to a control unit typically include the datapath's status outputs.

A control unit is either programmable or not. The programmable type acts upon a sequence of instructions stored in RAM or ROM. These instructions are decoded and used in combination with the control unit's inputs to determine its operation. To sequence instructions, the control unit will need a loadable counter, sometimes known as a program counter or an instruction pointer, to hold the memory address of the next instruction to be executed. The non-programmable type has its operation determined only by its current state and inputs.


Mano, M. Morris, and Kime, Charles R. Logic and Computer Design Fundamentals. 2nd Edition. Prentice Hall, 2000.