Short Question And Answer Microprocessor Set-6

1.What is meant by keyboard debouncing?
Key bouncing may cause multiple entries made for the same key. To overcome this problem after a key press is sensed the device is made to wait for few milliseconds. Then the key is checked again to ensure it is still pressed. If it is still pressed it is taken as a valid key press. This process is called keyboard debouncing.

2.What are the functions performed by Intel 8251?
8251 is used for converting parallel data to serial data or vice versa. The data transmission or reception can either be asynchronous or synchronous. It is used to interface MODEM and establish serial communication through
MODEM over telephone lines.

3.What are the primary features of 8259?

  •  8259 manages 8 interrupt requests (IR0 to IR7)
  •  8259 can solve eight levels of interrupt priorities in a variety of modes.
  •  With additional 8259 devices, the priority scheme can be expanded to  64 levels.
  •  8259 is designed to operate only with 8-bit processors. 8259A is designed to operate only with 8 bit as well as 116 bit processors.

4.What is the function of SM2 bit present in SCON register in 8051?

  • SM2 enables the multiprocessor communication feature in modes 2 and 3. If SM2=1, RI will not be activated if the received 9th data bit is 0.
  • In mode 1, if SM2=1, RI will not be activated if a valid stop was not received.
  • In mode 0, SM2 should be 0.

5.If a 12MHz crystal is connected with 8051, how much is the time taken for
the count in timer 0 to get incremented by one?
Baud rate = Oscillator frequency/12 = 12Mhz/12 = 1 microsecond

6.What is the advantage of microcontroller over microprocessor?
1. The overall system cost is low, as the peripherals are integrated in a single chip.
2. The system is very small.
3. The system is easy to troubleshoot and maintain.
4. If required additional RAM, ROM and I/O ports may be interfaced.
5. The system is more reliable.

7.What is the need for D/A converter?
The microcontrollers can produce only digital signals. Analog signals are needed for controlling certain analog devices in many applications. The Digitalto-Analog converters are used to convert the digital signal to analog signal.

8.What is the time duration for one state and one machine cycle if a 6 MHz
crystal is connected to 8051?
Clock frequency=6 MHz/2=3 MHz
One T state= 1/ Clock frequency=1/3 MHz= 0.333 microsec
The time taken to execute a machine cycle is 12 clock periods.

9.What is the difference between timer and counter operation in 8051?
The timer counts the internal clock pulses whose frequency is 1/12th of oscillator frequency.
The counter counts the internal clock pulses, which are given through T0 pin (for counter 0) and T1 pin (for counter 1) of 8051.

10.What is the function of IP register in 8051?
The IP register is used to set high priority to one or more interrupts in 8051.
– – – PS PT1 PX1 PT0 PX0
Setting a bit to make the corresponding interrupt to have high priority and setting a bit 0 makes the corresponding interrupt to low priority.

11.What is the importance of special function registers available in 8051
The 8051 operations that do not use the internal 128-byte RAM address from 00H to 7FH are done by a group of special internal registers, SFRs, which may be addressed like internal RAM.

12.What is the job of TMOD register?
TMOD register is used to set the various timer operation modes. TMOD is dedicated solely to the two timers (Timer 0 & 1) and can be considered to be two duplicate 4-bit registers, each of which controls the action of the timers.

13.Name the interrupts of 8051 microcontroller.

  • External interrupt-0
  • External interrupt-1
  • Timer-0 interrupt
  • Timer-1 interrupt
  • Serial port interrupt

14.What is the function of DPTR register?
The data pointer register is the 16-bit address register that can be used to fetch any 8-bit data from the data memory space. When it is not being used for this purpose, it can be used as two eight registers, DPH and DPL.

15.What are the functions of 8051 microcontroller?

  • 8 bit CPU with registers A and B
  • 16 bit PC and DPTR
  • 8 bit PSW
  • 64K Program memory
  • 64K data memory
  • 128 bytes of on-chip data memory
  • 32 I/O pins for port0, port1, port2 and port3
  • Two 16 bit timers,T0 and T1
  • Full duplex UART: SBUF
  • Two external and three internal interrupt sources.\

16.What happens in power down mode of 8051 microcontroller?
The memory locations of power down RAM can be maintained through a separate small battery backup supply so that the content of these RAM can  be preserved during power failure conditions.

17. Define Watch Dog Timer.
Watch Dog Timer is a dedicated timer to take care of system malfunction. It can be used to reset the controller during software malfunction, which is referred to as “Hanging”. A microcontroller will have facility for enabling or
disabling the watchdog timer. When the WDT is enabled, it will initiate a hardware reset whenever it overflows. In order to avoid a reset during normal condition, the software should take care of clearing WDT well before its overflow.

18. Define Baud rate.
Baud rate is used to indicate the rate at which data is being transferred.
Baud rate=1/Time for a bit cell.

19. List some of the applications of microcontroller.

  • Building control (Fire detection)
  • Industrial control (Process control)
  • Motor speed control (Stepper motor control)
  • Handheld instruments (Digital level meter)
  • Peripheral devices (Printer)
  • Stand alone devices (Color Xerox machine)
  • Automobile applications (Power steering)
  • Home applications (Washing machine)
  • Instrument sub functions (Spectrum Analyzer)

20. What are the basic units of a microprocessor?
The basic units or blocks of a microprocessor are ALU, an array of registers and control unit.