1. Digital Electronics Understanding truth tables

2. AND gate How many lines did a 2-input AND gate truth table have? ABZ (output) 000 010 100 111 Answer:4

3. AND gate What about if you have a 3 input AND gate? How many lines does our truth table have now? ABCZ (output) 0000 0010 0100 0110 1000 1010 1100 1111

4. And Gate You will have noticed that 0s and 1s are used in a truth table. This is known as a ‘binary’ number system. There are only two types of digit.

5. AND gate ABCZ (output) 0000 0010 0100 0110 1000 1010 1100 1111 Each row represents a decimal number (i.e. the numbers we normally use – 1,2,3,4,5… 9 Number of 1s Number of 2s Number of 4s Decimal equivalent of this row is “5” – i.e. a “4” plus a “1”

6. AND gate So from the table we see that 001 means decimal “1” and 101 means decimal “5”. The maximum value was 111 on the table, but what would 1111 mean in decimal? Answer: 8 + 4 + 2 + 1 15