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Digital Electronics
Y
A
(a)
B
A
(b)
B
Y=A+B
A
0
0
1
1
B
0
1
0
1
Y
1
0
0
0
(c)
Figure 4.16 (a) Two-input NOR implementation using an OR gate and a NOT circuit, (b) the circuit symbol of
a two-input NOR gate and (c) the truth table of a two-input NOR gate.
In general, the Boolean expression for a NOR gate with more than two inputs can be written as
Y = A + B + C + DDDDD
(4.6)
4.3.7 EXCLUSIVE-NOR Gate
EXCLUSIVE-NOR (commonly written as EX-NOR) means NOT of EX-OR, i.e. the logic gate that
we get by complementing the output of an EX-OR gate. Figure 4.17 shows its circuit symbol along
with its truth table.
The truth table of an EX-NOR gate is obtained from the truth table of an EX-OR gate by
complementing the output entries. Logically,
Y = A ⊕ BB = AAB + AABB
(4.7)
(a)
Y=A B
+
B
A
A
0
0
1
1
B
0
1
0
1
Y
1
0
0
1
(b)
Figure 4.17 (a) Circuit symbol of a two-input EXCLUSIVE-NOR gate and (b) the truth table of a two-input
EXCLUSIVE-NOR gate.