Q. Draw the general block diagram of microprocessor. Explain the function of each block.

Microprocessor is a programmable digital electronic device that incorporates the functions of a central processing unit (CPU) into a single IC package. 

  • Microprocessors are general-purpose devices used in many applications. 
  • Microprocessor contains the ALU (Arithmetic and Logical Unit), Control Unit and Registers. 
  • Typical microprocessor operations include addition, subtraction, multiplication, division, comparing two numbers, and fetching data from memory or I/O device. 
  • These operations are performed using a set of instructions that is part of the microprocessor design.
  • The 8085, 80286, 80386, 80486, Pentium are the example of Intel Microprocessor and 68000 series from Motorola.

Three basic features differentiate microprocessors :

1. Instruction set : The set of instructions that the microprocessor can execute.

2. Bandwidth : The number of bits processed in a single instruction.

3. Clock speed : Given in Megahertz (MHz) or Gigahertz, the clock speed determines how many instructions per second the processor can execute. 

The general block diagram of microprocessor is shown in Figure

General Block Diagram of Microprocessor
General Block Diagram of Microprocessor
  • Arithmetic Logic Unit (ALU) : The arithmetic and logical unit (ALU) performs arithmetic operations such as addition, subtraction, multiplication and or division and logical operation such as AND, OR, NOT and XOR needed to carryout the instructions. 
  • Instruction decode and Control Unit (CU) : This unit is responsible for fetching instructions from main memory and finding out the meaning of the instruction and operands required for operation .
  • Microprocessor Instruction register (IR) : The function of the instruction register is to store the instruction that is being executed at the time . An instruction register is part of the CPU's control unit. 
  • Program Counter (PC) : A program counter is a register in a microprocessor that contains the address of the next instruction being fetched while executing current instruction. As each instruction gets fetched,the program counter is incremented by 1 and points to the next instruction to be fetched. When the computer restarts or reset, the program counter normally set to 0. 
  • Registers : Register is a small high speed memory and consists of a set of binary storage cells called flip-flops with parallel reading or writing or both the facilities. 
  • The size of register in the term bits depends on the size of the data. Microprocessor reads data from one of the registers for performing the arithmetic or logical operation. Once the operation is over, microprocessor stores the result in a register. Data are usually loaded from memory to register. Similarly the resultant data will be loaded from registers to memory.

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