PRACTICE EXAM 3 PROBLEM 3 SOLUTION
1250
F 14
EX:
Using only 2-input logic gates, i.e., AND, NAND, OR, NOR, XOR, or XNOR,
design a logic circuit with the following truth table:
A
0
0
0
0
1
1
1
1
SOL'N:
Inputs
B
0
0
1
1
0
0
1
1
C
0
1
0
1
0
1
0
1
Output
Y
0
1
0
1
1
1
0
1
The output equals C except for A=1, B=0, and C=1, in which case the
output should also be 1.
Y = C + A⋅B
(1)
Note that we do not need to include C in the second term, since we want
Y=1 whether B=0 or B=1. To invert B, we use a NAND gate with inputs
tied together.