Microcontrollers – Question and Answer

1. What are the advantages of micro controller over microprocessor?
  1. The overall system cost is low, as the peripherals are integrated in a single chip.
  2. The size 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.
2. What happens in power down mode of 8051 micro controller?

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.

3. What is the function of DPTR register?

The data pointer register (DPTR) 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 bit registers, DPH and DPL.

4. What is the possible branching range when an AJMP/ACALL of 8051 instruction is executed?

2 K bytes

5. Give the difference between the microprocessor and microcontroller.
Microprocessor Microcontroller
The functional blocks: ALU, Registers, Timing & Control unit Microprocessor functional blocks + Timer, Memory, I/O ports, ADC, DAC
Used for general purpose applications Used for special purpose applications
Number of instructions are high Few instructions can do the functions
Number of bit manipulating instructions are low Number of bit manipulating instructions are high
Costly and large size Cheap and small size
6. Define watch dog time.

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 refered to as “Hanging”. A microcontroller will have facility for enabling or disabling the watch dog 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.

7. List the interrupts of 8051 micro controller.

External interrupt – 0
External interrupt – 1
Timer – 0 interruput
Timer – 1 interruput
Serial Port interruput

8. What is 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 Digital to Analog converters are used to convert the digital signal to analog signal.

9. What is the time duration for one state and one machine cycle if a 6Mhz crystal is connected to 8051?

Clock frequency = 6 MHz / 2 = 3MHz
One T state = 1/ clock frequency = 1/ 3 MHz = 0.333 micro sec
The time taken to execute a machine cycle is 12 clock periods.

10. 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.

11. 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.


IP register

Setting a bit to make the corresponding interrupt to have high priority and setting a bit 0 makes the corresponding interrupt to low priority.

12. What is the importance of special function registers available in 8051 microcontroller?

The 8051 operations that do not use the internal 128 byte RAM address from 00H to 7F H are done by a group of special internal registers, SFRs (Special Function Registers), which may be addressed like internal RAM.

13. What is the job of the TMOD register?

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

14. What are the features of 8051 microcontroller?
  • 8 bit CPU with registers A and B
  • 16 bit PC and DPTR
  • 8 bit PSW
  • 64 K Program memory
  • 64 K Data memory
  • 128 bytes of on-chip Data memory
  • 32 I/O pins for Port 0 , Port 1 , Port 2 and Port 3
  • Two 16 bit Timers, T0 and T1
  • Full duplex UART : SBUF
  • Two external and three internal interrupt sources.
15. 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.

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Santhakumar Raja

Hi, This blog is dedicated to students to stay update in the education industry. Motivates students to become better readers and writers.

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