Exclusive or AND Nor Gates
A less common but still important gate is called an exclusive oR gate, abbreviated as XoR. An XOR gate has only two inputs, unlike the OR gate, which may have several inputs. However, the XOR is similar to the OR gate in that it generates a 1 output if either input is a 1. The exclusive OR is different when both inputs are 1s or 0s. In that case, the output is a 0.
The symbol for an XOR gate is shown in Figure 42-12. Also shown is the equivalent logic circuit. Figure 42-13 shows the truth table for an XOR gate. The algebraic output is written as Y 5 A!B. It is read as “Y equals A exclusive or B.”
The complement of the XOR gate is the XNoR (exclusive NoR) gate. Its symbol is shown in Figure 42-14. The bubble on the output implies inversion or complement.
Also shown is the equivalent logic circuit. Fig- ure 42-15 shows the truth table for an XNOR gate. The algebraic output is written as Y 5 A!B, read as “Y equals A exclusive nor B.”
Questions
1. What is the difference between an OR gate and an XOR gate?
2. Draw the symbol used to represent an XOR gate.
3. Develop a truth table for an XOR gate.
4. Draw the symbol used to represent an XNOR gate.
5. Write the algebraic expressions for XOR and XNOR gates.