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Architecture of 8085 microprocessor
  • Last Updated : 25 Mar, 2021

8085 is an 8-bit, general purpose microprocessor. It consists of following functional units:- 

  1. Arithmetic and Logic Unit (ALU) :
    It is used to perform mathematical operations like: addition, multiplication, subtraction, division, decrement, increment, etc.
     
  2. Flag Register :
    It is an 8-bit register that stores either 0 or 1 depending upon which value is stored in the accumulator.
     
  3. Accumulator :
    Accumulator is used to perform I/O, arithmetic and logical operations. It is connected to ALU and internal data bus. 
     
  4. General Purpose Registers :
    There are 6 general purpose registers. These registers can hold 8 bit values. These  8-bit registers are B,C,D,E,H,L. These registers work as 16-bit registers when they work in pair like: B-C, D-E, H-L.
     
  5. Program Counter : 
    Program Counter holds the address value of the memory to the next instruction that is to be executed. It is a 16-bit register.
     
  6. Stack Pointer :
    It works like stack. In stack ,the content of register is stored that is later used in the program. It is a 16-bit special register.
     
  7. Temporary Register :
    It is a 8-bit register that holds data values during arithmetic and logical operations.
     
  8. Instruction register and decoder :
    It is a 8-bit register that holds the instruction code that is being decoded. The instruction is fetched from the memory. 
     
  9. Timing and control unit :
    The timing and control unit comes under the CPU section, and it controls the flow of data from CPU to other devices. It is also used to control the operations performed by the microprocessor and the devices connected to it. There are certain timing and control signals like: Control signals, DMA Signals, RESET signals, Status Signal. 
     
  10. Interrupt control :
    Whenever a microprocessor is executing a main program and if suddenly an interrupt occurs, the microprocessor shifts the control from the main program to process the incoming request. After the request is completed, the control goes back to the main program. There are 5 interrupt signals in 8085 microprocessors: INTR, TRAP, RST 7.5, RST 6.5, RST 5.5
     
  11. Address bus and data bus : 
    Data bus is bidirectional and carries the data which is to be stored.  Address bus is unidirectional and carries location where data is to be stored.
  12. Serial Input/output control :
    It controls the serial data communication by using Serial input data and Serial output data.
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