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REGISTERSCOMPONENTS
REGISTERS
STACK POINTER
Stack
Stack Pointer
A stack is a means of storing data that works on a ‘Last in first out’ (LIFO) basis. It reverses the order that data arrives and is sent.
REGISTERS
PROGRAM COUNTER
Program Counter
Instruction 5
Instruction 4
Instruction 3
Instruction 2
Instruction 1Program Counter
Points to the next instruction that needs to be fetched and executed.
REGISTERS
STATUS REGISTER
• positive number• negative number• overflow result• zero
Status Register
The status register holds condition codes to indicate the outcome of operations. For example, an arithmetic operation may produce a positive, negative, zero or overflow result , so a flag is set accordingly.
REGISTERS
ACCUMULATOR
Accumulator
Control Unit
Holds the result of the current set of instructions . For example, ADD #45 which means add the number 45 to the current contents in the accumulator and store the result in the accumulator.
Arithmetic Logic Unit (ALU)
REGISTERS
CURRENT INSTRUCTIONREGISTER (CIR)
Current Instruction
Instruction 4
Instruction 3
Instruction 2
Instruction 1Current Instruction Current
Instruction Register
Holds the current instruction to be executed while it is decoded and executed.
Address Data #
Address Data #
REGISTERS
MEMORY ADDRESS REGISTER (MAR)
Address Data #
Address Data #
Address Data #
Address Data #This holds the address of the memory location currently being accessed by the processor. It stores memory addresses of instructions and data.
REGISTERS
Control unit
Data #
Data #
Data #
Data #
Data #
Data #The control unit is a component of a computer's central processing unit (CPU) that directs operation of the processor. It tells the computer's memory, arithmetic/logic unit and input and output devices how to respond to a program's instructions.
REGISTERS
MEMORY DATA REGISTER (MDR)
Data #
Data #
Data #
Data #
Data #
Data #This holds the data being transferred to and from memory and currently being acted upon by the processor.
REGISTERS
Arithmetic Logic Unit (ALU)
Instructions & Data
Arithmetic Logic Unit (ALU)
An arithmetic logic unit(ALU) is a digital circuit that performs integer arithmetic and logical operations. The ALU is a fundamental building block of the central processingunit of a computer, and even the simplest microprocessors contain one for purposes such as maintaining timers.
