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Micro Controller Interview Questions - Part 3


Write a program to swap two numbers using 8051 ?

MOV A,# data
SWAP A

Write a program to subtract two numbers & exchange the digits using 8051 ?

MOV A,#9F MOV R0,#40
SUBB A,R0
SWAP A

What are the different types of Address decoding Techniques ?

  • Absolute decoding/Full decoding
  • Linear decoding/Partial decoding

    Comparison between full address decoding and Partial address decoding ?

    Full address decoding
  • All higher address lines are decoded to select the memory or I/O device.
  • More hardware is required to design decoding logic.
  • Higher cost for decoding circuit.
  • No multiple addresses.
  • Used in large systems. Partial address decoding
  • Few higher address lines are decoded to select the memory or I/O device.
  • Hardware required to design decoding logic is less and sometimes it can be elimibated
  • Less cost for decoding circuit.
  • It has a disadvantage of multiple addresses. (Shadow addresses)
  • Used in small systems.

    What is the significance of wait state generator ?

    This is used to transfer data between slower I/O device and the microprocessor. In some applns, the speed of I/O systems is not compatible with the microprocessor’s timings. So the microprocessor has to confirm whether the peripheral is ready or not. If READY pin is high, the peripheral is ready otherwise 8085 enters in to wait state.

    What is a Non-maskable interrupt ?

    It is unaffected by any mask or interrupt enable. Eg: TRAP

    What is a Data pointer register ?

    The data pointer register (DPTR) consists of a high byte(DPH) and a low byte (DPL) functions to hold 16 bit address. It may be manipulated as a 16-bit data register or as independent 8-bit registers. It serves as a base register in indirect jumps, look up table instructions and external data transfer.

    What are the operating modes of 8279 ?

    1. Input modes
  • Scanned keyboard
  • Scanned sensor matrix
  • Strobed input 2.Display modes
  • Left entry (Type writer mode)
  • Right entry (Calculator mode)

    What are the different functional units in 8279 ?

  • CPU interface section
  • Keyboard section
  • Display section
  • Scan section

    What are the priority modes in 8259 ?

  • Fully nested mode
  • Special fully nested mode c. Rotating Priority mode
  • Special Masked mode e. Polled mode

    Micro Controller Interview Questions - Part 4 >>>




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