Operation of a NOR Gate
A NOR gate produces a LOW output when any of its inputs is HIGH. Only when all of its
inputs are LOW is the output HIGH. For the specific case of a 2-input NOR gate, as shown
in Figure 3-33 with the inputs labeled A and B and the output labeled X, the operation can
be stated as follows:
For a 2-input NOR gate, output X is LOW when either input A or input B is HIGH,
or when both A and B are HIGH; X is HIGH only when both A and B are LOW.
This operation results in an output level opposite that of the OR gate. [n a NOR gate, the
LOW output is the active or asserted output level as indicated by the bubble on the output.
Figure 3-34 illustrates the operation of a 2-input NOR gate for all four possible input com-
binations, and Table 3-9 is the truth table for a 2-input NOR gate.
Operation of a NAND Gate
A NAND gate produces a LOW output only when all the inputs are HIGH. When any of
the inputs is LOW, the output will be HIGH. For the specific case of a 2-input NAND gate,
as shown in Figure 3-25 with the inputs labeled A and B and the output labeled X, the op-
eration can be stated as follows:
For a 2-input NAND gate, output X is LOW only when inputs A and B are HIGH;
X is HIGH when either A or B is LOW, or when both A and B are LOW.
Note that this operation is opposite that of the AND in terms of the output level. In a NAND
gate, the LOW level (0) is the active or asserted output level, as indicated by the bubble on
the output. Figure 3-26 illustrates the operation of a 2-input NAND gate for all four input
combinations, and Table 3-7 is the truth table summarizing the logical operation of the 2-
input NAND gate.
The Exclusive-OR Gate
Standard symbols for an exclusive-OR (XOR for short) gate are shown in Figure 3-41. The
XOR gate has only two inputs. The output of an exclusive-OR gate is HIGH only when the two inputs are at opposite
logic levels. This operation can be stated as follows with reference to inputs A and Band
output X:
For an exclusive-OR gate. output X is HIGH when input A is LOW and input B is
HIGH, or when input A is HIGH and input B is LOW: X is LOW when A and B
are both HIGH or both LOW.
The four possible input combinations and the resulting outputs for an XOR gate are il-
lustrated in Figure 3-42. The HIGH level is the active or asserted output level and occurs
only when the inputs are at opposite levels. The operation of an XOR gate is summariLed
in the truth table shown in Table 3-] I.
المادة المعروضة اعلاه هي مدخل الى المحاضرة المرفوعة بواسطة استاذ(ة) المادة . وقد تبدو لك غير متكاملة . حيث يضع استاذ المادة في بعض الاحيان فقط الجزء الاول من المحاضرة من اجل الاطلاع على ما ستقوم بتحميله لاحقا . في نظام التعليم الالكتروني نوفر هذه الخدمة لكي نبقيك على اطلاع حول محتوى الملف الذي ستقوم بتحميله .
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