Compound Gates
There are two operations that have the same logic as AND
or OR gates, but with an
inverted output. The NAND operation says if and
only if all inputs are on, the output will be off. The output will be on if any of the inputs are
off. The NOR operation says if any input is on,
the output will be off. Notice the bubble on the
output of the schematic symbol used to indicate an inversion.
|
NAND (all high = low,
else high)
|
|
Input 1
|
Input 2
|
Output
|
|
0
|
0
|
1
|
|
0
|
1
|
1
|
|
1
|
0
|
1
|
|
1
|
1
|
0
|
|
| |
|
NOR (any high = low,
else high)
|
|
Input 1
|
Input 2
|
Output
|
|
0
|
0
|
1
|
|
0
|
1
|
0
|
|
1
|
0
|
0
|
|
1
|
1
|
0
|
|
| |
There is a variation on the OR logic called Exclusive
OR or XOR. Exclusive OR says the
output will be on if the inputs are different.
Another one, the inverter or NOT operation, says that the output will be opposite
in state to the input. It obviously has only one input and one output. Note that
it will change an AND to a NAND, an OR to a NOR and an XOR to a NXOR if
connected to their outputs. It simply changes 1s to 0s and 0s to 1s.
| XOR (different =
high, same = low) |
| Input 1 |
Input 2 |
Output |
| 0 |
0 |
0 |
| 0 |
1 |
1 |
| 1 |
0 |
1 |
| 1 |
1 |
0 |
 | | |