Friday 5 April 2019

GE 6252 Two Marks Questions & Answers - Unit 4

GE 6252 BASIC ELECTRICAL AND ELECTRONICS ENGINEERING 
UNIT 4 DIGITAL ELECTRONICS
TWO MARK QUESTIONS & ANSWERS 


Question 1: Draw the symbol and give the truth table of AND, OR and NOT gate.
Answer: The symbol, expression and truth table of AND, OR and NOT gates are, 


Question 2: Draw the symbol of XNOR gate and give its truth table.
Answer: The symbol and truth table of XNOR gate are,










Question 3: Prove the following: A + ĀB = A + B
Answer: A + ĀB = (A + Ā) (A + B)          
             [ By Distributive Law: A + Ā = 1; 1 . A = A ]
               A + ĀB = 1 . (A + B)
               A + ĀB = A + B.

Question 4: What are the universal gates?
Answer: NAND gate and NOR gate are universal gates. Both the gates can be used alone to construct the basic logic functions (AND, OR, NOT) or any combination of these functions.

Question 5: Implement AND and OR gates using NAND gate.
Answer: The AND and OR gates are implemented using NAND gates as follows,
Question 6: Implement the Boolean expression Y = AB + AC + BC using NAND gates.
Answer:


Question 7: State the differences between combinational and sequential circuits.
Answer: The differences between combinational and sequential circuits are tabulated:
Combinational Circuits
Sequential Circuits
The output of the combinational circuit depends on the present combination of inputs.
The output of the sequential circuits depends on the present inputs and past outputs.
There is no memory element in combinational circuits.
Memory elements are present in sequential circuits to store information.
Example: Half adder, Full adder.
Example: Counter, Register.
Question 8: What is the difference between the half adder and full adder?
Answer: The differences between the half adder and full adder are tabulated:
HALF ADDER
FULL ADDER
Half adder is a logic circuit that adds two one-bit binary numbers.
Full adder is a logic circuit that adds two one-bit binary numbers with a carry bit.
No such possibilities exist for the half adder.
A full adder circuit can be obtained by combining two half adder with an OR gate.

Question 9: What is a flip flop?
Answer: Flip flop is a device that exhibits two stable states. It is used as a basic memory element in a binary system. It is capable of storing one-bit data.

Question 10: Name the four different types of flip flop?
Answer: The four different types of flip flops are,
  • RS flip flop,
  • D flip flop,
  • JK flip flop,
  • T flip flop.

Question 11: What is the race-around condition?
Answer: In a JK flip flop, when the clock pulse is applied and J = K= 1, the flip flop is in toggle mode. The outputs keep toggling indefinitely during a single clock pulse making the output uncertain. This multiple toggles is called race-around condition.

Question 12: What is a register?
Answer: A register is a group of flip flops and it is capable of storing a binary number. Registers are used in digital systems including a microprocessor.

Question 13: What is a shift register?
Answer: A register is a group of flip flops. If the output of each flip flop is connected to the input of the adjacent flip flop, then the circuit is called a shift register.
For each successive clock pulse, the data bits are moved from one flip flop to another depending on how the flip flops are connected.

Question 14: How are shift registers classified?
Answer: The shift registers are classified as, 
  • Serial In Serial Out (SISO) shift register,
  • Serial In Parallel Out (SIPO) shift register,
  • Parallel In Serial Out (PISO) shift register,
  • Parallel In Parallel Out (PIPO) shift register.

Question 15: What is a decade counter?
Answer: A decade counter is a counter that has the capability to count up to 10 states.

Question 16: Mention the two types of D/A converters.
Answer: The two types of D/A converters are,
  • Binary weighted resistor D/A converter and
  • R-2R ladder network D/A converter.



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