Logic Gates, Level II

Welcome back for another round with logic gates. If you haven’t already read Logic Gates, Level I, please do so in order to make sure you are fully caught up. Moving along…

The next gate we will look at is the “NOR” gate. This gate is essentially like the opposite of the “AND” gate in that both inputs must be 0 in order for the output to be 1, or true. Here is the truth table to demonstrate the “NOR” gate:

Input A: 0 | Input B: 0 | Output Q: 1
Input A: 0 | Input B: 1 | Output Q: 0
Input A: 1 | Input B: 0 | Output Q: 0
Input A: 1 | Input B: 1 | Output Q: 0


A “NOR” gate in “Distinctive Shape” symbolic illustration

Following the “NOR” gate on our list is the “NAND” gate, which outputs a 1 only if the inputs are not both 1. This can be thought of as “not and” in that a 0, or false, is output when both values are a 1, or true. Here is the truth table for “NAND”:

Input A: 0 | Input B: 0 | Output Q: 1
Input A: 0 | Input B: 1 | Output Q: 1
Input A: 1 | Input B: 0 | Output Q: 1
Input A: 1 | Input B: 1 | Output Q: 0


A “NAND” gate in “Distinctive Shape” symbolic illustration

After that, we have the “XOR” gate, which outputs 1, or true, strictly when only one input is a 1 or 0. Therefore, the other must be a 0 or 1, respectively. The “exclusive or” gate determines if both outputs are different. Here is the truth table showing the results:

Input A: 0 | Input B: 0 | Output Q: 0
Input A: 0 | Input B: 1 | Output Q: 1
Input A: 1 | Input B: 0 | Output Q: 1
Input A: 1 | Input B: 1 | Output Q: 0

Notice that when both values are the same, such as 0 & 0 and 1 & 1, the output is 0, or false.


A “XOR” gate in “Distinctive Shape” symbolic illustration

Finally, we will wrap up this section with the “XNOR” gate, which does the opposite of the “XOR” gate in that it determines if both inputs are the same. If both inputs are 0, or both inputs are 1, then the output will be 1, or true. Otherwise, it is 0, or false. Here is the truth table:

Input A: 0 | Input B: 0 | Output Q: 1
Input A: 0 | Input B: 1 | Output Q: 0
Input A: 1 | Input B: 0 | Output Q: 0
Input A: 1 | Input B: 1 | Output Q: 1


A “XNOR” gate in “Distinctive Shape” symbolic illustration

That wraps up Logic Gates, Level II. Most of the basics of the logic gates has now been covered, but there is more to learn about the symbolic representation and implementation of gates in the next levels.

Good luck!

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