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Electronics and Communication Engineering - Digital Electronics

Exercise : Digital Electronics - Section 2
21.
The Boolean expression for the circuit of the given figure
A {F + (B + C) (D + E)}
A [F + (B + C) (DE)]
A + F + (B + C) (D + E)]
A [F + (BC) (DE)]
Answer: Option
Explanation:

B and C in parallel give B + C. Similarly D and E in parallel give D + E. (B + C) in series with (D + E) give (B + C) (D + E). Since F is in parallel we get F + (B + C) (D + E). Finally A is in series. Therefore we get A[F + (B + C) (D + E)].

22.
What will be BCD number when the output is 0.37 V?
00110111
10110111
11001000
01001000
Answer: Option
Explanation:

BCD number is (00110111).

23.
The first machine cycle of an instruction is always
a memory read cycle
a fetch cycle
a input/output read cycle
a memory write cycle
Answer: Option
Explanation:

Fetch cycle is always first machine cycle.

24.
A counter has N flip flops. The total number of states are
N
2 N
2N
4 N
Answer: Option
Explanation:

One flip-flop means 2 states and N flip-flops means 2N states.

25.
Out of S, R, J, K, Preset, Clear inputs to flip flops, the synchronous inputs are
S, R, J, K only
S, R, Preset, Clear only
Preset, Clear only
S, R only
Answer: Option
Explanation:

Preset and clear inputs are not applied in any fixed sequence.

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