Everything Science Grade 12

CHAPTER 14. ELECTRONICS 14.5

Occupied

Hot

Output

Example 4: Solving a circuit with two logic gates

QUESTION

Compile the truth tablefor the circuit below.

SOLUTION

Firstly, we label the inputs A and B. We also label the point where the twogates

are connected C.

A

B

C Output

Next we prepare a truthtable. There is a column for each of the inputs, for

the intermediate point Cand also for the output.The truth table has fourrows,

since there are four possible inputs — 00, 01, 10and 11. Next we fill in the C

column given that we know what a NOR gate does.

A B C Output

0 0 1

0 1 0

1 0 0

1 1 0

Next, we can fill in the output, since it will always be the opposite of C (because

of the NOT gate).