# Digital Circuits (Test 2)

## Gate Exam : Ec Electronics And Communication Engineering

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Digital Circuits
| Digital Circuits |
Q.1
The output Y of the logic circuit given below is

A. 0
B. 1
C. X
D.
Explaination / Solution:

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Q.2
The following binary values were applied to the X and Y inputs of NAND latch shown in the figure in the sequence indicated below :
X =    ,Y =    X =    ,Y =    X =    Y =
The corresponding stable P Q, output will be

A. P = ,Q = P = ,Q = P = ,Q = or P = ,Q =
B. P = ,Q = P = ,Q = or P = ,Q = P = ,Q =
C. P = ,Q = P = ,Q = P = ,Q = or P = ,Q =
D. P = ,Q = P = ,Q = P = ,Q =
Explaination / Solution:
No Explaination.

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Q.3
Consider the following circuit which uses a 2-to-1 multiplexer as shown in the figure below. The Boolean expression for output F in terms of A and B is

A.
B.
C. A + B
D.
Explaination / Solution:

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Q.4
An 8085 assembly language program is given below.
Line 1:   MVI A, B5H
2:   MVI B, OEH
3:   XRI 69H
5:   ANI 9BH
6:   CPI 9FH
7:   STA 3010H
8:   HLT
After execution of line 7 of the program, the status of the CY and Z flags will be
A. CY = 0, Z = 0
B. CY = 0, Z = 1
C. CY = 1, Z = 0
D. CY = 1, Z = 1
Explaination / Solution:
No Explaination.

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Q.5
The output expression for the Karnaugh map shown below is

A.
B.
C.
D.
Explaination / Solution:

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Q.6
What are the counting states (Q1,Q2) for the counter shown in the figure below

A. 11,10,00,11,10,...
B. 01,10,11,00,01...
C. 00,11,01,10,00...
D. 01,10,00,01,10...
Explaination / Solution:

The given circuit is as follows.

The truth table is as shown below. Sequence is 00, 11, 10, 00 ...

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Q.7
Consider the given circuit.

In this circuit, the race around
A. does not occur
B. occurs when CLK = 0
C. occurs when CLK = 1 and A = B = 1
D. occurs when CLK = 1 and A = B = 0
Explaination / Solution:

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Q.8
An 8085 executes the following instructions 2710 LXI H, 30A0 H 2713 DAD H 2414 PCHL All address and constants are in Hex. Let PC be the contents of the program counter and HL be the contents of the HL register pair just after executing PCHL. Which of the following statements is correct ?
A. PC = 2715H HL = 30A0H
B. PC = 30A0H HL = 2715H
C. PC = 6140H HL = 6140H
D. PC = 6140H HL = 2715H
Explaination / Solution:

2710H LXI H, 30A0H ; Load 16 bit data 30A0 in HL pair 2713H DAD H ; 6140H ⟶ HL 2714H PCHL ; Copy the contents 6140H of HL in PC Thus after execution above instruction contests of PC and HL are same and that is 6140H

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Q.9
If segments a to g are considered as functions of P1 and P2, then which of the following is correct

A.
B.
C.
D.
Explaination / Solution:

LED d is 1 all condition and also it depends on
d = c + e

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Q.10
The logical gate implemented using the circuit shown below where. V1 and V2 are inputs (with 0 V as digital 0 and 5 V as digital 1) and Vout is the output is

A. NOT
B. NOR
C. NAND
D. XOR