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Internal architecture of 8085 microprocessor

To work with microprocessor 8085, first we have to know the internal architecture of 8085 microprocessor. Internal architecture of 8085 microprocessor tells us the relation between different working blocks of 8085 microprocessor. Generally microprocessor consists of different working units.

Working Blocks 

  • Control unit: It control complete operations of microprocessor.
  • ALU: It performs data processing function in respect of arithmetic and logical manner.
  • Registers: It provide internal storage to CPU.
  • Interrupts: It maintain priority of process.
  • Internal data bus: It use to transfer data to appropriate place.

In my early post, I discussed on pin configuration of 8085 microprocessor. You may also read that. It will definitely help you to understand the Internal architecture of 8085 microprocessor. In bellow you can see the block diagram of internal architecture of 8085 microprocessor.

Block Diagram

Internal architecture of 8085 microprocessor

Lets we start to brief discussion on all individual units of 8085 microprocessor.

The ALU:

The ALU stands for arithmetic and logical unit. As name suggest all the arithmetic and logical operation of microprocessor done inside this unit. In addition to the arithmetic & logic circuits, the ALU not only includes the accumulator, which is part of every arithmetic & logic operation. But also, it includes a temporary register used for holding data temporarily during the execution of the operation. But mind it, this temporary register is not accessible by the programmer.


Register is a very vital unit of 8085 microprocessor. These registers are used in different purpose. Mainly registers are three types.

  • General Purpose Registers
  • Special Purpose Registers.
  • Temporary Registers.

 General Purpose Registers are by name B, C, D, E, H& L. All are 8 bit registers. It can used as individually Or can be used as 16 bit register pairs like BC, DE and HL. H & L can be used as a data pointer which holds memory address. But it cannot make pair like BE, DC. So it should be in pair like BC, DE and HL.

Internal architecture of 8085 microprocessor

Special Purpose Registers:

In 8085 microprocessor there have lots of special purpose register which have specific task. In bellow you find those special purpose register.

Accumulator (8 bit register):

Accumulator is very important register in 8085 microprocessor. It store 8 bit data in size. All the arithmetic and logical operation done inside the accumulator. And it should remember that after execution of an operation, generated result will store inside it. It also used to store 8 bit data during I/O transfer.

Flag Register:

Flag is a brain of a microprocessor. It is an 8 bit register. It shows the status of the microprocessor before and after an operation. In 8085 microprocessor have five flags. Those are S (sign flag), Z (zero flag), AC (auxiliary carry flag), P (parity flag) & CY (carry flag).

Program Counter (PC):

Program counter is also a special purpose register. This is a register that is used to control the sequencing of the execution of instructions. This register always holds the address of the next instruction. Since it holds an address so it must be a 16 bits register.

Stack pointer:

As the name suggest stack pointer used as an address pointer. The stack pointer is also a 16-bit register. It used to point into memory. The memory, this register points to a special area called the stack. The stack is an area of memory used to hold data that will be retrieved soon. The stack is usually accessed in a Last In First Out (LIFO) fashion.

Let’s check how you learn “Internal architecture of 8085 microprocessor” with a simple quiz.

8085 Architecture

Architecture of 8085 microprocessor

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Hi myself Subham Dutta, having 15+ years experience in filed of Engineering. I love to teach and try to build foundation of students. Try to make them imagine what they learn.

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