Electronics and Communication Engineering - Digital Electronics

21. 

An AND gate has two inputs A and B and one inhibit input 3, Output is 1 if

A. A = 1, B = 1, S = 1
B. A = 1, B = 1, S = 0
C. A = 1, B = 0, S = 1
D. A = 1, B = 0, S = 0

Answer: Option B

Explanation:

All AND inputs must be 1 and inhibit 0 for output to be 1.


22. 

The greatest negative number which can be stored is 8 bit computer using 2's complement arithmetic is

A. - 256
B. - 128
C. - 255
D. - 127

Answer: Option B

Explanation:

The largest negative number is 1000 0000 = -128.


23. 

A JK flip flop has tpd= 12 ns. The largest modulus of a ripple counter using these flip flops and operating at 10 MHz is

A. 16
B. 64
C. 128
D. 256

Answer: Option D

Explanation:

Number of flip-flops = = 8.333 say 8

Modulus = 28 = 256.


24. 

The basic storage element in a digital system is

A. flip flop
B. counter
C. multiplexer
D. encoder

Answer: Option A

Explanation:

Storing can be done only in memory and flip-flop is a memory element.


25. 

In a ripple counter,

A. whenever a flip flop sets to 1, the next higher FF toggles
B. whenever a flip flop sets to 0, the next higher FF remains unchanged
C. whenever a flip flop sets to 1, the next higher FF faces race condition
D. whenever a flip flop sets to 0, the next higher FF faces race condition

Answer: Option A

Explanation:

In a ripple counter the effect ripples through the counter.