22/03/2020

Counter Interview Question Answer - 3


31
Explain the term : Loading of counter


Loading of counter
  • The presetting of the counter is called as loading of the counter.


32
Describe the function of look ahead carry? Why it is necessary?


Function of look ahead carry
  • The output of the up counter is called as carry.
  • This carry is brought forward to next stage by AND gate therefore the output of the counter Q and output of the proceeding counter is given at the input of AND gate.
  • The output of the rightmost AND gate is not valid if the output of the all proceeding AND gates are valid.
  • The propagation delay of each AND gates accumulate and it limits the speed of the counter.
  • The counter is available in the form of ICs in order to increase the speed of it is called as look ahead carry.


33
What is hybrid counter?


Hybrid counter
  • It is a counter in which the output of a synchronous counter drives the clock input of another counter to get divide by N operation.


34
What is self starting of the counter?


Self starting of the counter
  • The self starting of the counter is one which eventually enters its proper sequence regardless of its initial state.


35
Explain the term : Programmable counter


Programmable counter
  • It is a counter available in the IC form.
  • It can be pre loaded with binary number in parallel form prior to initiation of counting.
  • This pre loading capable the counter to counter from 0 to any number. Such counter is called as programmable counter.


36
How the asynchronous loading of the counter is done?


The asynchronous loading of the counter is done by initial state is loaded using direct SET and direct CLEAR inputs on the flip flops.

37
How the synchronous loading of the counter is done?


The synchronous loading of the counter is done by occurrence of clock pulse using JK inputs on the flip flops.

38
Describe the difference between synchronous and asynchronous counters.


Asynchronous counters
  • They are serial counters.
  • They are slow because each flip flop can change its state if the preceding flip flop changes their state.
  • The propagation delay time is accumulated.
  • The propagation delay can cause glitches.
  • The asynchronous counter may skip some of state if the clock frequency is high.
  • Slow speed as compared to synchronous counter

Synchronous counters
  • All the flip flops are triggered simultaneously by clock pulses in the synchronous counter.
  • As all the flip flops are triggered simultaneously, the propagation delay time do not accumulate.
  • The glitches may produce due to difference between propagation delay of individual flip flop and difference between value of clock pulse time from high to low ( tPHL ) and clock pulse time from low to high ( tPLH ).
  • The operating frequency of the synchronous counter is much higher than that of asynchronous counter.
  • As the number of flip flop increases, it will not affect the operation of the counter.
  • High speed
  • Less decoding problems
  • More complex circuit than asynchronous counter


39
What is shift register counter?


Shift register counter
  • It is built by serial in serial out shift register.
  • The shift register counter is constructed by providing feedback from output of the last flip flop to the input of the first flip flop.


40
Describe the types of shift register counter. 


Types of shift register counter
  • Basic ring counter
  • Johnson counter ( Twisted ring counter )


40
Which type of flip flop is used for the construction of the ring counter?


D flip flop OR JK flip flop

41
What is reason behind the name of Ring counter?


Ring counter
  • The Q output of the each flip – flop stage is connected to the input of the next stage but Q output of the last stage is connected to the input of the first stage.
  • Therefore the array of flip flops is arranged in a ring therefore it is called as ring counter.


42
How many bits are counted by N – bit ring counter and N – bit ripple counter?
              OR
Why the ripple counter is economical to that of the ring counter?


The N – bit ring counter count only n bits whereas the N – bit ripple counter counts 2n bits therefore the ripple counter is economical to that of the ring counter.

43
Describe the three advantages of ring counter as compared to ripple counter.


Advantages of ring counter over ripple counter
  • It does not require decoder.
  • Fast operation
  • It is synchronous operation and requires no gates external to flip flops.


44
What is other name of Johnson counter?


Twisted ring counter, switch – tail ring counter

45
Which type of shift register is used in the Johnson counter?


Serial in serial out shift register




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