Anna University

Digital Logic Circuits (DLC)

Important Questions

Common To
EE46:Digital Logic Circuits

EC1261A Digital Logic Circuits

080280029:Digital Logic Circuits

131405:Digital Logic Circuits

10133EE406A:Digital Logic Circuits

Unit I
1. Obtain the minimum SOP using Quine McCluskey’s method and verify using K – Map.

F = m0 + m2 + m4 + m8 + m9 + m10 + m11+ m12 + m13

2. Determine the prime implicants of the following function using tabulation method and verify using K –Map. F = (A,B,C,D) = ∑ (3,4,5,7,9,13,14,15)

3. Design a Binary to BCD code converter and BCD to Excess -3 code converter.

4. Reduce the given expressions using Boolean algebra:

(1) x’y’z’ + x’y’z + x’yz + xy’z + xyz

(2) p’q’r + p’qr’ + p’qr + pqr’ + pq’r’

5. Design a decimal adder to add two decimal digits.

Unit II
1. Design a asynchronous decade counter using JK flipflop.

2. Design a 8 X1 Mux using 2 X1 multiplexers.

3. Design a synchronous counter using JK flipflop in the sequence 7,4,3,1,5,0,7….

4. Draw and explain the block diagram of Mealy circuit

5. Design a MOD -5 synchronous counter using JK flip-flops .Draw a timing diagram.

6. Design a 2 bit Magnitude Comparator.

Unit III
1. Describe the steps involved in design of asynchronous sequential circuit in detail with an example.

2. Explain the working of a 3 – input TTL totem-pole NAND gate.

3. Explain the concept and implementation of ECL logic family.

4. Explain In detail about FPGA.

5. A combinational circuit is defined by the functions .

F1 (A,B,C ) =∑ (3,5,6,7)

F2 (A,B,C ) =∑ (0,2,4,7).Implement the circuit with PLA

Unit IV
1. Design an asynchronous sequential circuit that has two inputs X2 and X1 and one output Z. When

X1 = 0, that output Z is 0. The first change in X2 that occurs while X1 is 1 will cause output Z to be 1. The output Z will remain 1 until X1 returns to 0.

2. An asynchronous sequential circuit has two internal states and one output. The excitation and

output functions describing the circuit are

Y1 = x1x2 + x1 y’2 + x’2y1

Y2 = x2 + x1 y’1y2 + x’1y1

Z = x2 + y1

a) Draw the logic diagram of the circuit.

b) Derive the transition table and output map.

c) Obtain a flow table for the circuit.

3. The Circuit has two inputs T (toggle) and C (clock) and one output Q. The output state is complemented if T=1 and clock C changes from 1 to 0 otherwise, under any other input condition, the output Q remains unchanged. Derive the primitive flow table and implication table and the logic diagram.

4. Draw the State diagram and obtain the primitive flow table for a circuit with two inputs X1 and X2 and two outputs Z1 and Z2 that satisfies the following conditions.

1) When X1 X2 =00, output Z1 Z2 =00.

2) When X1 = 1 and X2 change from 0 to 1, the output Z1 Z2 =01.

3) When X2 = 1 and X1 change from 0 to 1, output Z1 Z2 =10.

4) Otherwise output does not change.

5. Implement the following Boolean functions with a PLA.

F1 (A, B, C) = ∑ (0, 1, 2, 4)

F2 (A, B, C) = ∑ (0, 5, 6, 7)

F3 (A, B, C) = ∑ (0, 3, 5, 7)

Unit V
1. Write VHDL program for 4x1 multiplexer.

2. Explain in detail the design procedure for register transfer language.

3. Write an HDL behavioral description of JK flip-flop using if-else statement based on the value of present state.

4. Write VHDL program for 4-bit ripple counter.

5. Explain the design procedure of RTL using VHDL