Microprocessor Design/Control Unit

The control unit reads the opcode and instruction bits from the machine code instruction, and creates a series of control codes to activate and operate the various components to perform the desired task.

Simple Control Unit
In its most simple form, a control unit can take the form of a lookup table. The machine word opcode is used as the index into the table, and the various control signals are output to the respective destinations.

Complex Control Unit
A more complex version of a control unit is implemented as a finite state machine (FSM). Multi-cycle, pipelined, and other advanced processor designs may require an FSM-based control unit.