The inputs of a control unit are Clock, Instruction register, flags and control signals from control bus. The outputs are the control signals within the processor and the control signals to the control bus.
The inputs are explained below
Clock: This is how the control unit “keeps time.” The control unit causes one micro-operation (or a set of simultaneous micro-operations) to be performed for each clock pulse. This is sometimes referred to as the processor cycle time, or the clock cycle time.
Instruction register: The opcode of the current instruction is used to determine which micro-operations to perform during the execute cycle.
Flags: These are needed by the control unit to determine the status of the processor and the outcome of previous ALU operations.
Control signals from control bus: The control bus portion of the system bus provides signals to the control unit, such as interrupt signals and acknowledgments.
The outputs are explained below
Control signals within the processor: These are two types; those that cause data to be moved from one register to another, and those that activate specific ALU functions.
Control signals to control bus: These are also of two types: control signals to memory, and control signals to the I/O modules.