Introduction to 8085 Microprocessor and its components

Introduction to 8085 Microprocessor and its components

May 31, 2018

The word “micro” means extremely small.  It means the microprocessor solve the problem by the small IC. The microprocessor read the instructions by the memory and executes the problems line by line. The microprocessor performs arithmetic and logical operation. That operation done by the ALU (Arithmetic Logical Unit). It is in large CPU (Center processing Unit). In 8085 mp used 6,500 Transistors and it’s produce From 1975 to 1990s.

Arithmetic Logical Unit:

ALU is used for arithmetic and logical operation in microprocessor. The logical operations means like OR, NOR, AND, NAND and NOT etc are call logical operations. And also the arithmetic operations means like ADD, SUB, DIV and MULT etc are the arithmetic operations. It includes upcode, instruction, instruction set etc.

the Bus,  a group of lines pins or signal having same working function is defines a bus. There is two types of bus first is the data bus and second one is the the system bus.

Architecture Diagram of 8085 Microprocessor

Fig: Architecture Diagram of 8085 Microprocessor


In fig, shows the architecture diagram of 8085 microprocessor describes the,


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


  • 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.

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.

Flag Registers

  •  micro processor have five flip-flop  flag register. these are change the status according to the result stored in an accumulator. Which  are following:
    • carry flip-flop(C)
    • sign flip-flop(S)
    • zero flip-flop(Z)
    • parity flip-flop(P)
    • auxiliary flip-flop(AC)

Program counter : it stores the memory address of the next instruction to be executed. Also it is 16-bit register used as memory pointer.

Timing and control unit: it help the mp in to provides timing and control signal to perform the various operation.ALE,RD and WR.

Bus structure of 8085 microprocessor

Fig: Bus structure of 8085 MP.

In fig, shows Bus structure of 8085 MP describes the,

Address Bus:

=> Mp has 16 bit address bus, the bus over which the center processing unit sends out the address of the memory location is known as Address bus. The address bus carried the location of the memory to written or read form.

Data bus:

=> Mp has  8-bit data bus. It store the 8-bit data. It is bidirectional as Microprocessor requires to send or receive data.

Control bus:

=> Control bus used for the control the memory location.  The  control bus overall control the data input and output. When signal comes in mp then control bus handle this signal and process by their type.

Pin Diagram of 8085 Microprocessor

Fig: Pin diagram of 8085 MP.

In fig, shows Pin diagram of 8085 MP describes the,
1.Address bus, Data bus, Control and status signals

Address bus A8­- A15 carries the most significant 8-bits of memory of I/O address. Data bus is AD7-AD0 carries the least significant 8-bit address and data bus.These signals are used to identify the nature of operation. There are 3 control signal and 3 status signals.Three control signals are RD, WR & ALE.

2. IO/M

This signal is used to differentiate between IO and Memory operations, i.e. when it is high indicates IO operation and when it is low then it indicates memory operation.

3.S1 & S0

These signals are used to identify the type of current operation.

4. Power supply

There are 2 power supply signals − VCC & VSS. VCC indicates +5v power supply and VSS indicates ground signal.

5. Clock signals

There are 3 clock signals

  • X1
  • X2

6. Interrupts & externally initiated signals

  • INTA
  • HOLD
  • HLDA (HOLD Acknowledge)


7. Serial I/O signals

  • SOD
  • SID