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## Exclusive-logic-gates

THE EXCLUSIVE OR GATE

The exclusive OR gate is a modified OR gate that produces a HIGH output when only one of the inputs is HIGH. You will often see the abbreviation X-OR used to identify this gate. When both inputs are HIGH or when both inputs are LOW, the output is LOW.

The standard symbol for an exclusive OR gate is shown in the figure below along with the associated Truth Table. The operation function sign for the exclusive OR gate is Å.

Exclusive OR gate and Truth Table.

If you were to observe the input and output signals of an X-OR gate, the results would be similar to those shown in the figure below. At T0, both inputs are LOW and the output is LOW. At T1, A goes to HIGH and remains HIGH until T2. During this time the output is HIGH. At T3, B goes HIGH and remains HIGH through T5. At T4, A again goes HIGH and remains HIGH through T5. Between T3and T4 , the output is HIGH. At T4, when both A and B are HIGH, the output goes LOW.

Exclusive OR gate timing diagram.

THE EXCLUSIVE NOR GATE

The exclusive NOR (X-NOR) gate is nothing more than an X-OR gate with an inverted output. It produces a HIGH output when the inputs are either all HIGH or all LOW. The standard symbol and the Truth Table are shown in the figure below. The operation function sign is Å with a vinculum over the entire expression.

Exclusive NOR gate and Truth Table.

A timing diagram for the X-NOR gate is shown in the next figure. You can see that from T0 to T1, when both inputs are LOW, the output is HIGH. The output goes LOW when the inputs are opposite; one HIGH and the other LOW. At time T3, both inputs go HIGH causing the output to go HIGH.

Exclusive NOR gate timing diagram.

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