Logic functions and Minimization

Question 71

The output of a tristate buffer when the enable input in 0 is

• Always 0
• Always 1
• Retains the last value when enable input was high
• Disconnected state

Question 72

If the maximum output voltage of a DAC is V volts and if the resolution is R bits then the weight of the most significant bit is

• V/ (2^R -1)
• (2^R-1).V/(2^R-1)
• (2^R-1).V
• V/(2^R-1)

Question 73

Consider the logic circuit given below. The inverter, AND and OR gates have delays of 6, 10 and 11 nanoseconds respectively. Assuming that wire delays are negligible, what is the duration of glitch for Q before it becomes stable?

• 5
• 11
• 16
• 17

Question 74

Which of the following is not valid Boolean algebra rule?

• X.X = X
• (X + Y).X = X
• X ̄ + XY = Y
• (X + Y).(X + Z) = X + YZ

Question 75

Which of the following logic expressions is incorrect?

• 1 ⊕ 0 = 1
• 1 ⊕ 1 ⊕ 1 = 1
• 1 ⊕ 1 ⊕ 0 = 1
• 1 ⊕ 1 = 0

Question 76

Which logic gate is used to detect overflow in 2\'s complement arithmetic?

• OR gate
• AND gate
• NAND gate
• XOR gate

Question 77

Any set of boolean operators that is sufficient to represent all boolean expressions is said to be complete. Which of the following is not complete?

• {NOT, OR}
• {NOR}
• {AND, OR}
• {AND, NOT}

Question 78

The most simplified form of the boolean function, x (A,B,C,D) = Σ (7,8,9,10,11,12,13,14,15) (expressed in sum of minterms) is?

• A + A\'BCD
• AB + CD
• A + BCD
• ABC + D

Question 79

How many programmable fuses are required in a PLA which takes 16 inputs and gives 8 outputs? It has to use 8 OR gates and 32 AND gates.

• 1032
• 776
• 1284
• 1536

Question 80

The voltage ranges for a logic high and a logic low in RS-232 C standard is

• Low is 0.0V to 1.8V, High is 2.0V to 5.0V
• Low is -15.0V to -3.0V, High is 3.0V to 15.0V
• Low is 3.0V to 15.0V, High is -3.0V to -15.0V
• Low is 2.0V to 5.0V, High is 0.0V to 1.8V