CS302 - Digital Logic Design
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Q & A
Short Question & Answers
Q40: Explain Combinational Function Devices?
Digital circuits are formed by the combination of Logic Gates. Xor, Xnor, NAND, NOR are combinational function devices.
Q41: Differentiate between hexadecimal and octal number system.
Octa decimal use Base 8 whereas Hexa decimal use Base 16.
Q42: One of the ABEL entry methods uses logic equation. Explain at least two examples?
ABEL however is case sensitive, thus variable „A‟ is treated separately from variable „a‟. All ABEL equations must end with „;‟.
X = AB(bar)C + (ABC)bar + AB + B(bar)C
Y = (A(bar)+B+C(bar)+D)(A+B+C)

X = A& !B & C # !A & !B & !C # A & B # !B & C;
Y = (!A # B # !C #D) & (A # B # C);
Q43: Draw function table of a half adder circuit?
Q44: Draw the function table of 2-to-4 decoder.
Q45: Explain 8-input Multiplexer with the help of circuit Diagram and Function Table.

Q46: Half adder explanation its function table Boolean expression and circuit diagram.
Half-Adder: A Half-Adder can be fully described in terms of its Function table, its Sum and Carry Out Boolean Expressions and the circuit Implementation.

Half-Adder Function Table: The Half-Adder has a 2-bit input and a 2-bit output. The function table of the Half-Adder has two input columns representing the two single bit numbers A and B. The function table also has two output columns representing the Sum bit and Carry Out bit.

Half-Adder Sum & Carry Out Boolean Expressions: The Sum and Carry Out expressions of the Half-Adder can be determined from the function table. The Half-Adder Sum and Carry Out outputs are defined by the expressions

Q47: Explain Tri-State Buffers with the help of block diagram.
Tri-State Buffer is a NOT gate with a control line that disconnects the output from the input. When the control line is high the buffer operates like a NOT gate and when the control line is low the output is disconnected from the output and high impedance is seen at the output. Tri-state buffers are used to disconnect the outputs of devices which are connected or share a common output line.

Course Instructor

Dr. Waseem Ikram
PhD Electrical Engineering
University of Manchester

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