DIGITAL ELECTRONICS MCQS PART 07

DIGITAL ELECTRONICS MCQS PART 07

1. How many flip-flops are required to construct mod 30 counter
(A) 5    
(B) 6        
(C) 4    
(D) 8
Ans: A
Explanation: Mod - 30 counter +/- needs 5 Flip-Flop as 30 < 25 Mod - N counter counts total ' N ' number of states.
To count 'N' distinguished states we need minimum n FlipFlop's as [N = 2n] For eg. Mod 8 counter requires 3 Flip-Flop's (8 = 23)

2. How many address bits are required to represent a 32 K memory
(A)10 bits.
(B)  12 bits.     
(C) 14 bits.
(D)  16 bits.
Ans: D
Explanation: 32K = 25 x 210 = 215,
Thus 15 address bits are required, Only 16 bits can address it.

3. The number of control lines for 16 to 1 multiplexer is
(A) 2.    
(B) 4.       
(C) 3.    
(D) 5.
Ans: B Explanation: As 16 = 24, 4 Select lines are required.

4. Which of following requires refreshing?
(A)SRAM.    
(B) DRAM.     
(C) ROM.    
(D) EPROM.
Ans: B

5. Shifting a register content to left by one bit position is equivalent to
(A)division by two.
(B) addition by two.
(C) multiplication by two.    
(D) subtraction by two.
Ans:C

6. The decimal equivalent of (1100)2 is
(A) 12    
(B) 16      
(C) 18    
(D) 20
Ans: A
Explanation: (1100)2 = (12)10

7. The binary equivalent of (FA)16 is
(A) 1010 1111    
(B)  1111 1010   
(C) 10110011    
(D)  none of these
Ans: B
Explanation: (FA)16 = (11111010)10

8.The output of SR flip flop when S=1, R=0 is
(A) 1    
(B) 0   
(C) No change    
(D)  High impedance
Ans: A
Explanation: As for the SR flip-flop S=set input R=reset input ,when S=1, R=0, Flip-flop will be set.

9. The number of flip flops contained in IC 7490 is
(A) 2.    
(B) 3.   
(C) 4.    
(D) 10.
Ans: A

10. The number of control lines for 32 to 1 multiplexer is
(A) 4.    
(B) 5   
(C) 16.    
(D) 6.
Ans: B
Explanation: The number of control lines for 32 (25) and to select one input among them total 5 select lines are required.