# 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

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

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.

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