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.
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