Free notes of the operating system some imp questions

 1. ALU 

2. STACK POINTER

3. PROGRAM COUNTER

4. INSTRUCTION REGISTER AND DECODER

ALU ( ARITHMATIC AND LOGIC UNIT )

It is 8 bit unit 

In this arithmetic and logical operation are carried out .

ALU contain the binary adder to perform addition substracion by 2’s complement method

Data is supplied by memory devices and input ouput devices

The result is typically stored in the accumulator.

STACK POINTER:-

Stack poiointer is a 16 bit register which contain the address of top of stack

With the help of incrementer and decrementer stack pointer perform their work

The stack pointer is incremented when data is push 

The stack pointer is decrementd when data is pop.

INSTRUCTION REGISTER AND DECODER :-

During the instruction fetch, the first 8 bit of instruction is transfer to the 8 bit instruction register

The content of instruction register are available to the instruction decoder

The output of decoder get by timing signals, ALU & data buffer.

PROGRAM COUNTER:-

Program counter is 16bit register acting a pointer to next executable instruction

It always contain the 16 bit address of memory location where next executable code is stored

Microprocessor uses this register to sequence the execution of instruction.

PC is a auto incremented pointer.

REGISTERS IN MICROPROCESSOR 8085

1. ACCUMULATOR

2. TEMPORARY REGISTER

3. INCREMENTER / DECREMENTER

4. REGISTER B & C

5. SERIAL I/O CONTROL

ACCUMULATOR:-

Accumulator is main 8 bit register in microprocessor 8085.

It is used to perform arithmetic and logical operation one of the operand is always stored in accumulator

It can be used as both primary source and destination register and the final result is always stored in accumulator

All data transfer between cpu and i/o devices are perform through accumulator. 

TEMPORARY REGISTER:-

The temporary register is used to stored the data during execution of arithmetic or logic instruction 

The register used internally 

This register is not available for the programmer

This one is very useful register of microprocessor 8085.

INCREMENTER/DECREMENTER:- 

It is 16 bit special purpose register 

It also used inn addition and substraction

It is used to add or substract one from the program counter or stack pointer.

REGISTER B/C:-

Register b and c this are the general purpose register 

It is 8 bit register but it can be also used as a 16 bit register 

The most significant 8 bit are stored in the register b and the least 8 bit are stored in register c .

This register are programmable register means programmer can used this rergister.

Thank you 

Keep study with us....,...