he Logic OR Function
The Logic OR Function function states
that an output action will occur or become TRUE if either one “OR” more
events are TRUE, but the order at which they occur is unimportant as it
does not affect the final result. For example, A + B = B + A. In Boolean algebra the Logic OR Function follows the Commutative Law the same as for the logic AND function, allowing a change in position of either variable.
The OR function is sometimes called by its full name of “Inclusive OR” in contrast to the Exclusive-OR function we will look at later in tutorial six.The logic or Boolean expression given for a logic OR gate is that for Logical Addition which is denoted by a plus sign, (+). Thus a 2-input (A B) Logic OR Gate has an output term represented by the Boolean expression of: A+B = Q.
Switch Representation of the OR Function
Then this type of logic gate only produces and output when “ANY” of its inputs are present and in Boolean Algebra terms the output will be TRUE when any of its inputs are TRUE. In electrical terms, the logic OR function is equal to a parallel circuit.
Again as with the AND function there are two switches, each with two possible positions open or closed so therefore there will be 4 different ways of arranging the switches.
OR Function Truth Table
| Switch A | Switch B | Output | Description |
| 0 | 0 | 0 | A and B are both open, lamp OFF |
| 0 | 1 | 1 | A is open and B is closed, lamp ON |
| 1 | 0 | 1 | A is closed and B is open, lamp ON |
| 1 | 1 | 1 | A is closed and B is closed, lamp ON |
| Boolean Expression (A OR B) | A + B | ||
