Q. Functional Requirements of a Control Unit?

Let's first try to define functions that a control unit should perform in order to get things to happen. However in order to define the functions of a control unit one should know what resources and means it has at its disposal. A control unit should know about the:  

(a)  Fundamental components of the CPU

(b)  Micro-operation this CPU performs.

CPU of a computer comprises the subsequent basic functional components: 

• The Arithmetic Logic Unit (ALU) that performs the basic arithmetic and logical operations.
• Registers that are used for information storage within the CPU.
• Internal Data Paths: These paths are useful for moving data between two registers or between a register and ALU.
• External Data Paths: Roles of these data paths are generally to link CPU registers with the memory or I/O interfaces. This role is generally fulfilled by system bus.
• The Control Unit: This causes all operations to occur in CPU.