Microprocessor Organization

ALU(Arithmetic Logic Unit)

• The part of a computer that performs all arithmetic computations, such as addition and multiplication, and all comparison operations. The ALU is one component of the CPU (central processing unit).
• To perform simple addition, subtraction, multiplication, division, and logic operation

Control Unit

• Control unit is circuitry that directs operations within the computer's processor by directing the input and output of a computer system.
•  A control unit works by gathering input through a series of commands it receives from instructions in a running programs and then outputs those commands into control signals that the computer and other hardware attached to the computer carry out.
• Example below :

Register

• A processor register is a local storage space on a processor that holds data that is being processed by CPU.
• Processor has a local storage area known as a register that performs most of the operations that the processor cannot perform directly.Any kind of data must first be identified by the register before it can be manipulated by the processor.

Accumulator

Accumulator is a AL register in which intermediate arithmetic and logic results are stored.Without a register like an accumulator, it would be necessary to write the result of each calculation (addition, multiplication, shift, etc.) to main memory, perhaps only to be read right back again for use in the next operation. 

                                    

Condition Code Register

• Contains flags set by the processor during the execution of instructions.Consists of individual bits are set or clear depending on the result of an operation. These bits can remember processing states between instruction.
• Different instruction affect the condition register in different way. Depend on processor type , a data , transfer instruction may not affect any flag , while an addition may affect several flag  

Program Counter

• The Program Counter (PC) is a register structure that contains the address pointer value of the current instruction. Each cycle, the value at the pointer is read into the instruction decoder and the program counter is updated to point to the next instruction
• Programmers do not have direct control over the program counter like they do with other registers. The program counter indicates where the CPU is in its current instruction sequence.

Stack Pointer

• The stack pointer is used to make sub-routines possible. By always pointing to the last used memory location, a push command can be used to add onto the stack and a pull to retrieve the last operation.
• Therefore, before executing a set of instructions, the current address can be pushed to the stack and at the end of the execution of the set of instructions, the address can be pulled from the stack making it possible to return to the previous location.
• The stack pointer must be initialized before it can be used.