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Micro Controller Interview Questions - Part 1


What is meant by micro controller ?

A device which contains the microprocessor with integrated peripherals like memory, serial ports, parallel ports, timer/counter, interrupt controller, data acquisition interfaces like ADC, DAC is called micro controller.

List the features of 8051 micro controllers ?

  • Single supply +5v operation using HMOS technology.
  • 4096 bytes program memory on-chip.
  • 128 data memory on chip.
  • 4 register banks
  • 2 multiple modes, 16 bit timer/counter
  • Extensive Boolean processing capabilities.
  • 64KB external RAM size.
  • 32 bi-directional I/O lines.

    Explain the operating mode 0 of 8051 serial port ?

    In this mode serial data enters and exists through RXD, TXD outputs the shift clock. 8-bits are transmitted or received:8-data bits(LSB first). The baud rate is fixed at 1/12 the oscillator frequency.

    Explain the operating mode 2 of 8051 serial port ?

    In this mode 11 bits are transmitted (through TXD) or received (through (RXD): a start bit(0), 8 data bits( LSB first), a programmable 9th data bit and a stop bit(1). On transmit, the 9th data bit can be assigned thevalue 0 or 1. On receive, the9th data bit go into the RB8 in special function register SCON, while the stop bit is ignored. The baud rate is programmable to either 1/32 or 1/64 the oscillator frequency.

    Explain the mode 3 of 8051 serial port ?

    In this mode, 11 bits are transmitted (through TXD) or (received (through RXD): a start bit(0), 8 data bits(LSB first), a programmable 9th data bit and a stop bit(1).It is same as mode 2 except the baud rate. The baud rate in mode 3 is variable.

    Explain the interrupts of 8051 micro controller ?

  • External interrupt 0 (IE0)
  • Highest priority
  • Timer interrupt 0 (TF0)
  • External interrupt 1 (IE1)
  • Timer interrupt 1 (TF1)
  • Serial port Interrupt
  • Receive interrupt (RI) - lowest priority
  • Transmit interrupt (TI)

    How many bytes of internal RAM and ROM supported by 8051 micro controller ?

    128 bytes of internal RAM and 4 bytes of ROM.

    Define machine cycle of 8051 ?

    8051 machine cycle consists of 6 states, S1 through S7. One state is made up of 2 clock pulses. Thus 12 clock period constitute one machine cycle. Two clock periods in a state is termed as phase 1 and phase 2.

    What are the special function of port 0 of 8051 ?

    Port 0 is used as a multiplexed low order address/data bus during the external memory access. When ALE is enabled, the address on port 0 pins are latched and bus is ready to act asa data bus when ALE is low.

    What are the alternative function of port 3 of 8051 ?

    Serial data input (P3.0), serial data output (P3.1), external interrupt 0 (P3.2), external interrupt 1 (P3.3), external input for timer 0(P3.4), external input for timer 1 (P3.5), external memory write pulse (P3.6), external memory read (P3.7) are the alternative functions of port 3.

    Micro Controller Interview Questions - Part 2 >>>




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