Digital-electronics 简明教程
Implementation of OR Gate from NOR Gate
OR 门是一个基本逻辑门，当任何输入为高时，它给出高或逻辑 1 输出。而 NOR 门是一个通用逻辑门，只有当所有输入为低或逻辑 0 时，它才给出高输出。在深入了解使用 NOR 门实现 OR 门之前，让我们首先讨论 OR 门和 NOR 门的基本理论。
An OR Gate is a basic logic gate that gives a HIGH or Logic 1 output, when any of its inputs is HIGH. Whereas, the NOR gate is a universal logic gate, which gives a HIGH output only when all its inputs are LOW or Logic 0. Before, going into the implementation of OR Gate using NOR Gate, let us discuss the basic theory of OR gate and NOR gate first.
What is an OR Gate?
OR Gate 是一个基本逻辑门。或门可以有两个或两个以上的输入，但只有一个输出。如果或门的任何一个输入处于高 (逻辑 1) 状态，则该或门会输出高 (逻辑 1)；否则，它会输出低 (逻辑 0) 状态。因此，仅当或门的所有输入都为低 (逻辑 0) 状态时，其输出才会为低 (逻辑 0) 状态。
An OR Gate is a basic logic gate. An OR gate can have two or more than two inputs, but has only one output. The OR gate gives a HIGH (Logic 1) output if any one of its inputs is in the HIGH or Logic 1 state, otherwise, it gives a LOW (Logic 0) state as output. Therefore, the output of the OR gate is LOW or Logic 0 state, only if all its inputs are LOW or Logic 0 state.
或门也称为 “ any or all gate ” 或 “ an inclusive OR gate ”。双输入或门的逻辑符号如图 1 所示。
The OR gate is also known as an "any or all gate" or "an inclusive OR gate". The logic symbol of a two input OR gate is shown in Figure-1.
如果变量 A 和 B 是或门的输入，而 Y 是输出变量，那么或门的输出方程按如下计算：
If variables A and B are the inputs to the OR gate and Y is the output variable, then the output equation of the OR gate is given by,
\mathrm{Y \: = \: A \: + \: B}
其中，‘+’ 符号表示或运算。它读作“Y 等于 A 或 B”。
Where, the '+' symbol represents the OR operation. It is read as "Y is equal to A OR B".
显示输入与或门输出之间关系的表格被称为或门的真值表。
The table that show the relationship between inputs and output of an OR gate is referred to as a truth table of the OR gate.
What is a NOR Gate?
NOR Gate 是一个通用逻辑门，因此它可用于实现任何其他类型的逻辑门。
NOR Gate is a universal logic gate, and hence it can be used for implementation of any other type of logic gate.
NOR 表示 NOT + OR。这意味着，或输出被否定或反转。因此，NOR 门是或门和非门的组合，即
NOR means NOT + OR. That means, the OR output is NOTed or inverted. Therefore, the NOR gate is a combination of OR gate and a NOT gate, i.e.,
\mathrm{NOR \:Gate \: = \:OR \: Gate \: = \: NOT \: Gate}
NOR 门是一种逻辑门，仅当其所有输入均为低 (逻辑 0) 时其输出才为高 (逻辑 1)，即使其任何输入变为高 (逻辑 1)，它也会输出低 (逻辑 0)。双输入 NOR 门的逻辑符号如图 2 所示。
A NOR gate is a type of logic gate whose output is HIGH (Logic 1), only when all its inputs are LOW (Logic 0), and it gives an output LOW (Logic 0), even if any of its inputs becomes HIGH (Logic 1). The logic symbol of a two input NOR gate is shown in Figure-2.
如果变量 A 和 B 是 NOR 门的输入变量，而 Y 是 NOR 门的输出变量，那么 NOR 门的输出按如下计算：
If variables A and B are the input variables to the NOR gate and Y is the output variable of the NOR gate, then the output of the NOR gate is given by,
\mathrm{Y \: = \: \overline{A \: + \: B} \: = \: (A \: + \: B)'}
“Y 等于 A 加 B 杠”。
It is read as "Y is equal to A plus B whole bar".
Implementation of OR Gate from NOR Gate
众所周知，NOR 门是一种通用逻辑门，因此仅使用 NOR 门，我们就可以实现或运算。使用 NOR 门的 OR 门逻辑图如图 3 所示。
As we know, the NOR gate is a type of universal logic gate, therefore, using NOR gates only, we can implement the OR operation. The logic diagram of OR Gate using NOR Gate is shown in Figure-3.
因此，从逻辑电路可以看出，我们仅需要两个 NOR 门来实现或运算。
Hence, from the logic circuit, it is clear that we require only two NOR gates for the realization of OR operation.
第一个 NOR 门对变量 A 和 B 执行 NOR 运算，因此第一个 NOR 门的输出为：
The first NOR gate performs the NOR operation on variables A and B, thus the output of the first NOR gate is,
\mathrm{Y_{1} \: = \: \overline{A \: + \: B}}
第二个 NOR 门对第一个 NOR 门的输出执行非运算。因此，第二个 NOR 门的输出为：
The second NOR gates perform the NOT operation on the output of the first NOR gate. Therefore, the output of the second NOR gate is,
\mathrm{Y \: = \: A \: + \: B}
这是或门的输出表达式。因此，我们仅可以使用 NOR 门（如图 3 所示）来实现或门。
This is the output expression of an OR gate. Therefore, we can realize an OR gate using NOR gates only as shown in Figure-3.