The three main elements of the control unit are:
1. Decoder
this is used to decode the instructions that create a program when they are being processed, and to establish in what actions must be taken in order to process them. These decisions are on average taken by looking at the opcode of the instruction, together with the addressing mode used. This is covered in better detail in the instruction execution section of this tutorial.
2. Control logic circuits
the control logic circuits are used to produce the control signals themselves, which are then sent around the processor. These signals report to the arithmetic & logic unit and the register array what they actions and steps they should be performing, what data they should be using to perform said actions, and what should be done with the outcomes.
3. Timer or clock
the timer or clock makes sure that all processes and instructions are carried out and finished at the right time. Pulses are sent to the other regions of the CPU at regular intervals (related to the processor clock speed), and actions only occur when a pulse is detected. This makes sure that the actions themselves also occur at these same regular intervals, meaning that the functions of the CPU are synchronized.