Friday, 7 December 2012

Architecture Diagram of 8085 Microprocessor

This is the functional block diagram of the 8085 Microprocessor.

This is the function
al Block Diagram of 8085 Microprocessor.

Acumulator:-It is a 8-bit register which is used to perform airthmetical and logical operation. It stores the output of any operation. It also works as registers for i/o accesses.

Temporary Register:-It is a 8-bit register which is used to hold the data on which the acumulator is computing operation. It is also called as operand register because it provides operands to ALU.

Registers:-These are general purposes registers. Microprocessor consists 6 general purpose registers of 8-bit each named as B,C,D,E,H and L.   Generally theses registers are not used for storing the data permanently. It carries the 8-bits data. These are used only during the execution of the instructions.
These registers can also be used to carry the 16 bits data by making the pair of 2 registers. The valid register pairs available are BC,DE HL. We can not use other pairs except BC,DEand HL. These registers are programmed by user.

ALU:-ALU performs the airthmetic operations and logical operation.

Flag Registers:-It consists of 5 flip flop which changes its status according to the result stored in an accumulator. It is also known as status registers. It is connected to the ALU.
There are five flip-flops in the flag register are as follows:
3.Auxiliary carry(AC)
The bit position of the flip flop in flag register is:


All of the three flip flop set and reset according to the stored result in the accumulator.
1.Sign- If D7 of the result is 1 then sign flag is set otherwise reset. As we know that a number on the D7 always desides the sign of the number.
if D7 is 1: the number is negative.
if D7 is 0: the number is positive.

2.Zeros(Z)-If the result stored in an accumulator is zero then this flip flop is set otherwise it is reset.

3.Auxiliary carry(AC)-If any carry goes from D3 to D4 in the output then it is set otherwise it is reset.

4.Parity(P)-If the no of 1's is even in the output stored in the accumulator then it is set otherwise it is reset for the odd.

5.Carry(C)-If the result stored in an accumulator generates a carry in its final output then it is set otherwise it is reset.

Instruction registers(IR):-It is a 8-bit register. When an instruction is fetched from memory then it is stored in this register.

Instruction Decoder:- Instruction decoder identifies the instructions. It takes the informations from instruction register and decodes the instruction to be performed.

Program Counter:-It is a 16 bit register used as memory pointer. It stores the memory address of the next instruction to be executed. So we can say that this register is used to sequencing the program. Generally the memory have 16 bit addresses so that it has 16 bit memory.
The program counter is set to 0000H.

Stack Pointer:-It is also a 16 bit register used as memory pointer. It points to the memory location called stack. Generally stack is a reserved portion of memory where information can be stores or taken back together.

Timing and Control Unit:-It provides timing and control signal to the microprocessor to perform the various operation.It has three control signal. It controls all external and internal circuits. It operates with reference to clock signal.It synchronizes all the data transfers.
There are three control signal:
1.ALE-Airthmetic Latch Enable, It provides control signal to synchronize the components of microprocessor.
2.RD- This is active low used for reading operation.
3.WR-This is active low used for writing operation.

There are three status signal used in microprocessor S0, S1 and IO/M. It changes its status according the provided input to these pins.


Serial Input Output Control-There are two pins in this unit. This unit is used for serial data communication.

Interrupt Unit-There are 6 interrupt pins in this unit. Generally an external hardware is connected to these pins. These pins provide interrupt signal sent by external hardware to microprocessor and microprocessor sends acknowledgement for receiving the interrupt signal. Generally INTA is used for acknowledgement. 

Register Section:-Many registers has been used in microprocessor. 


It consists of PIPO(Parallel Input Parallel Output) register.


aman srivastava said...

Very nice description. Well done n a grt thanxxxx.

Aman Srivastava.
iet lucknow

พงษ์พันธุ์ โปรณะ said...

Where's example code ? Sent to , please !!!

Raktim Laha said...

thank for sharing the nice post.

Reena John said...

very nice description......... thank you

rao harshitha said...

thankyou so much for your valuable notes its lucent

Shalin Siriwaradhana said...

What is the diagram software used to create these diagrams? Is it a online diagram tool , looking for one that works for Ubuntu.

Abhishek Kumar said...

thnkq for sharing notes..@abhishek from araah

Abhishek Kumar said...

thnkq for sharing notes..@abhishek from araah

Pradeep Yadav said...

very nice

Sonu Peter said...


udit said...

awesome point to point notes....thnx buddy.

Swati Gupta said...

Very nicely explained. It helped me a lot. Thank you

hashim malik said...

very nice intoduction..

Unknown said...

Awsome note its help to remember the points thanks bro..

Unknown said...

Superb description

anusha naidu said...

The best explanation ever . Thanks a lot buddy

Unknown said...

Explanation is best, but can u provide with PDF files

Shaikh Shaihzad Ahmed said...

Sukhriya itne behtareen andaaz ke explanation ke liye bhai...

Shaikh Shaihzad Ahmed said...

Sukhriya itne behtareen andaaz ke explanation ke liye bhai...

Unknown said...
This comment has been removed by the author.
saurabh poojary said...


saurabh poojary said...


Dave Ashwin said...

its superb explanation its too useful for us...

Ashwin B. Dave

Dave Ashwin said...

thnk you vrey much....

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