ABSTRACT
There are four basic logical operators, TRUE, NOT (or INVERT), AND and OR. The last three of these were described in Chapter 18. The first operator, TRUE is illustrated by its truth table:
The output equals the input. This is the symbol for a TRUE gate:
The -truth fables for AND, OR and some other commonly-used gates are shown below side by side for comparison. Reading from left to right, flie outputs are A AND B, A OR B, A EX-OR B, A NAND B, A NOR B and A EX-NOR B. The outputs for the last three gates are simply the inverse of the outputs of the first three. The truth tables are shown with two inputs, but gates can have more than two inputs. The truth fables for these can be worked out from the fable above.
