Unformatted text preview: Fig. 313 Truth tables for gates. AND and NAND Boolean expression for the AND gate (A  B)
and the NAND (A  B) is shown on the logic
diagram in Fig. 34th). The truth table for the NAN D gate is shown
at the right in Fig. 313. Notice that the truth
table for the NAND gate is developed by in
verting the outputs of the AND gate. The
AND gate outputs are also given in the table
For reference. NAND gates are commonly employed in
industrial practice and extensively used in
all digital equipment. Do you know the logic
symbol. Boolean expression. and truth table for the NAND gate? You must commit these
to memory. 35 THE NOR GATE The NOR gate is actually a NOT OR gate.
In other words. the output ofan OR gate is in
verted toformaNOR ate. The logic symbolv
for the NOR gate is diagramed in Fig.
3l4ta). Note that the NOR symbol is an OR
symbol with a small invert bubble tsrnall cir
cle} on the right side. The NOR function is
being performed by an OR gate and an in
verter in Fig. 3—th1. The Boolean espres— A
Y
B (a)
INPUTS
A A +3 ——
+ B
B A
to} Fig. 314 to) NOR gate logic symbol. (b) A
Boolean expression for the output of a NOR gate. Fig. 315 Truth table for OR and NOR gates. sion for the OR function (A + B) is shown.
The ﬁnal NOR function is given the Boolean
expression A + B. The truth table for the NOR gate is shown
at the right in Fig. 313. Notice that the
NOR gate truth table is just the complement
of the output of the OR gate. The output of
the OR gate is also included in the truth table
in Fig. 313 for reference. You now should memorize the symbol,
Boolean expression. and truth table for the
NOR gate. You will encounter these items
often in your work in digital electronics. 36 THE EXCLUSIVE
OR GATE The exclusive OR gate is sometimes referred
to as the “any but not all gate." The exclusive
OR gate is often shortened to the XOR gate.
The logic symbol for the XOR gate is dia
gramed in Fig. 3l6(a); the Boolean expression
for the XOR function is illustrated in Fig. 316(b). The symbol 63 means the terms are
XORed together. A truth table for the XOR gate is shown at
the right in Fig. 317. Notice that if any but A
Y
B (a) AjD—AoB
B (b) Fig. 316 (at) XOR gate logic symbol. (b) A
Boolean expression for the output of an XOR gate. INPUTS Binary Logic Gates
CHAPTER 3 NOR gate Exclusive OR gate 15 ...
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 Fall '05
 Myer,B

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