logic gates A combination of switches that performs a logical operation such as OR, AND, NOT, NOR etc.
For a switch the input/output voltage can be high or low. The high voltage can be denoted by `1' and low voltage by `0'. The truth table for the logic gates and the symbols used for their representation is shown in table LI and fig. l4 a-g.These logic gates are the basis of all logical decisions within a computer.
Table LI . Truth table for logic gates
|
|
Input |
Input |
output |
|
|
A |
B |
C |
|
OR |
0 |
1 |
1 |
|
|
1 |
0 |
1 |
|
|
1 |
1 |
1 |
|
|
0 |
0 |
0 |
|
|
|
|
|
|
AND |
1 |
0 |
0 |
|
|
0 |
1 |
0 |
|
|
0 |
0 |
0 |
|
|
1 |
1 |
1 |
|
|
|
|
|
|
NOT |
1 |
-- |
0 |
|
|
0 |
-- |
1 |
|
|
|
|
|
|
NOR = |
0 |
0 |
1 |
|
NOT+OR |
0 |
1 |
0 |
|
|
1 |
0 |
0 |
|
|
1 |
1 |
0 |
|
|
|
|
|
|
NAND= |
0 |
0 |
1 |
|
NOT+AND |
1 |
0 |
1 |
|
|
0 |
1 |
1 |
|
|
1 |
1 |
0 |
|
|
|
|
|
|
EXCLUSIVE OR |
0 |
0 |
0 |
|
|
0 |
1 |
1 |
|
|
1 |
0 |
1 |
|
|
1 |
1 |
0 |
|
|
|
|
|
|
EXCLUSIVE |
0 |
0 |
1 |
|
NOR |
0 |
1 |
0 |
|
|
1 |
0 |
0 |
|
|
1 |
1 |
1 |