Registers used in 8085 Microprocessor


Registers used in 8085 Microprocessor and their details

Registers Used-
(1) Simple register (main register)
(2)General purpose register
(3)Special function register
(4)Other register
1)Simple registers

a) Accumulator –

(A) 8 bit
(B) Used as a register for storing one data when two are  arithmetically and logically operated .
(C) after ALU operation result is also stored in accumulator.
(D) when single no is to be logically operated only accumulator is used as a storage as well as storing result after execution.
2) General purpose register-
(A)B,C,D,E,H &L are used  as general purpose register.
(B) Each 8 bit long .
(C)Pairing can also be done in a standard way to stored 16 bit data
eg (B-C, D-E, H-L)
(D) H-L pair is an exceptional pair which is used as a memory pointer to locate an address L X H 2000H.
H recognize H-L pair of general purpose register.
Load 16 bit data immediately in H-L pair it means 2000H is the location of memory where data is stored and it is recall by an instruction MOV A M
M locates memory  location 2000H which is pointed bye H-L pair.
Exceptional point in 8085 microprocessor 16 bit additional can only be possible by using an instruction DAD.

3) Special function register-
stack pointer & program counter are two special function register these are those register which are used only by microprocessor not by user.

a) Program counter-
(1) it is a 16 bit register
(2)Used by microprocessor
(3)It holds the address of next instruction to be executed for eg- after execution MOV A,B instruction program  counter will be automatically incremented and points next location of memory where another data to stored.

b) Stack pointer- It is used when interrupt is generated by microprocessor interrupt is a command which stop the main program counter location will be stored in a stack and program counter will be loaded with a new address through which sub routine is called.
Sub routine is a small program which is used many times by main program. For example- Generating delay in main program after execution of each instruction.

c) Stack
Small memory location acquired by main program in RAM area.

4) Other Registers-
1) Instruction Registers
2) Temporary Register

a) Instruction Registers-
1) 8 Bit long
2) It will store opcode (8 Bit) of an instruction.

b) Temporary register-
1) 8 Bit long
2) It will store the data temporary before execution of instruction.

Instruction decoder-
Bits generated by instruction registers will be decoded by instruction decode, It means digital signal will be converted in analog signals and these signals will be send to timing and control unit.

Timing and Control Unit-
Signals generated by instruction decoder will be provided by control by way using this unit.
For example-RD, WR, SID, SOD.
SID & SOD are known as Serial In data and Serial out Data.
For example- Copy data from pen drive to microprocessor and vice versa.

Address/Data Bus Buffer (AD0 to AD7)-
1) 8 bit bidirectional.
2) Address as well as data on the same bus.
3) Both data and address will be differentiating by clock cycle generated by timing and control unit.
4) First clock cycle will be loaded lower 8 bit address on the bus.
5) Two more clock cycle will load the data on address bus.

Address Bus buffer( A8 to A15)-
Higher order address bus unidirectional. Address latch 74373 will be used as temporary storage for lower bit of address. If address latch is high than address is high and vice versa.

8085 AH1 microprocessor is only microprocessor which operates at 6MHz frequency because of HMOS technology.



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