# Logic gates

Explanations about logic gates and what they can be used for

1. ### Supercap2F

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Mar 22, 2014
You might want to have the logic gate symbols next to there truth table.

Regards

Dan

2. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

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2,830
Jan 21, 2010
1 and 0 are not always represented by high and low respectively. high and low refer to the voltage level; true, false, 0, 1, on and off are abstract concepts that we can apply how we wish.

For example, consider inverted logic, or signals that are asserted when pulled low. In both cases you need to carefully consider what voltage level means "true" or "on".

As I said before, not all logic comes in the form of integrated circuits. Often we use logic functions without them.

Apart from the very long ans rambling sentence, you have an inaccuacy in that CMOS migh be preferred due to low power consumption (but that may not be true at high speeds) and CMOS may operate over a wider supply range, e.g. 3 to 15V as compared to 4.5 to 5.5V

As I said earlier, I've never heard it called a clocking notch. Can you provide a reference to that?

This needs to be earlier as you've already talked about high and low.

OK up to here...

That is rambling and not very informative.

As I mentioned earlier, you need to avoid conflating voltage levels with meanings. Logic gates are defined for positive logic, and you'll find that datasheets will explicitly state that high = 1 and low = 0 for the definition of their function. When you define a truth table, you can use 0 and 1 or true and false. When you talk about a physical gate you need to talk about high and low. It is the way that we assign high and low to 0 and 1 that define a gate as being nand or nor (for example)

But you need to remember that there can be more than one output.

There is no such thing as a schmitt gate. An input to a gate may have a schmitt trigger. And in some logic functions only select inputs will have them.

To talk about schmitt trigger inputs you have to mention hysteresis and you also need to have mentioned the valid input ranges for gates.

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