Q- Implement a basic ALU which performs the operations of logical AND, logical OR, ADD, SUBRACT depending on the values of S1 & S0 Ans: We need to use an ADDER, AND gate, OR gate and some MUXes to implement the above function. We select the functions using the two variables S0 & S1 as: S1 […]

# Combination Circuits

## Q9: Implement 4to1 MUX using 2to1 MUX

Q- Can we implement 4 to 1 MUX using (a) three 2 to 1 MUX (b) only two 2 to 1 MUX and a OR gate & NOT gate? Ans: (a) We can implement 4 to 1 MUX from 2 to 1 MUX as shown below: (b) We have already implemented 8 to 1 MUX using […]

## Q8: Implement function using MUX & ADDER

Q- Design and implement the following logical functions with a combinational circuit (with A and B being 4-bit numbers): S1 S0 Output 0 0 A OR B 0 1 A AND B 1 0 A’ 1 1 A XOR B Ans: The following circuit would give the required outputs:

## Q7: Implement function using MUX & ADDER

Q- Design and implement the following with a combinational circuit (with A and B being 4-bit numbers): S2 S1 S0 Output 0 0 0 2A 0 0 1 A plus B 0 1 0 A plus B’ 0 1 1 A minus 1 1 0 0 2A + 1 1 0 1 A plus B […]

## Q6: Implement function using MUX & ADDER

Q- Design and implement the following with a combinational circuit (with A and B being 4-bit numbers): S1 S0 Output 0 0 A plus B 0 1 left shift A 1 0 A plus B plus 1 1 1 2A + 1 Ans: We need one 4-bit parallel ADDER and MUX to implement the above. As […]

## Q5: Implement PALINDROME circuit

Q- Draw the circuit to check a PALINDROME number of even bits. Ans: Palindrome number (in bits) is the number which is same whether seen from the first and the last bit. E.g. 1001, 0110, 0000, 1111 in 4 bits So to check this we need to have same value of bit at 1st bit and […]

## Q4: Debug error in MUX

Q- Find out the situation when the following circuit of MUX 2 to 1 would not work as expected and how can we eliminate the error. Ans: When we have the static values at the inputs circuit would work fine but when ever there is a transition in the value of Select pin we have a situation […]

## Q3: Implement equations using Half Adders

Q- Implement the following equations using only Half Adder circuits. D= A XOR B XOR C E = A’BC + AB’C F = ABC’ + (A’+B’) C G= ABC Ans: We know the equations for Half Adder are S = A xor B and C = AB And can be represented as follow: We have […]

## Q2: Timing Diagram

Q- Now I make a certain change in the required output. The circuit is same as the previous question but it is not required to be AND gate anymore and output required is a HIGH pulse with width of 2 ns as: Now one has to choose the BLOCK such that we get the above […]

## Q1: Timing Diagram

Q- We are implementing a 3-input AND gate using the following circuit: We can replace BLOCK with number of (a) Buffers or (b) Inverters. The delay of buffer is Tp=2ns. Now we need to choose components such that we have proper output at F= X.Y.Z and the waveforms are as: Ans: Now if we orally […]