quick schematic help

[keebler303]

could someone tell me what it means when there are 3 inputs to a logic gate such as in this schematic?
thanks
Matt

[Madclicker]

Been 20 years since my freshman logics circuits, but this looks like a D flip flop. The gate you are asking about is a 3 input NOR.

[keebler303]

good memory madclicker. i didn't knwo there was such a thing as a three input nor. I've just been playing with some circuit stuff lately, mainly trying to drive a stepper motor with what I have in my elecctronics box, and that 3 input guy stood out as strange because i had never heard of it before.
Matt

[Al_The_Man]

With the 3 input nor, the output is only high when all three inputs are low, anything else and the output is low.
Al.

[lwill]

You can make a 3 input NOR out of 2 input ones:

[Madclicker]

Originally Posted by lwill You can make a 3 input NOR out of 2 input ones:

Or just use 3 input NOR gates. They used to come 3 to a chip.

[Madclicker]

Originally Posted by lwill You can make a 3 input NOR out of 2 input ones:

Also, isn't this just a NOT that Not's, therefore redundant?

[One of Many]

No, that not is not redundant. The true condition of a nor is only set when both inputs are 0.

In effect if you have 00 at the first one, the third one needs the inversion to make its output true(1) for the 000 inputs. Any other combination will be false(0).

DC

[Madclicker]

The first NOR is is just an OR and a NOT. I encircled the 2 NOTs. One from the first NOR and the one made from the second NOR. They are redundant. You can just replace the 2 NORs with 1 OR, but that won't get you any design awards, either. Like I said before, at the design level you would just use a 3 input NOR.

Logic circuits are hard enoungh to figure out when you use standard symbols....just look at that D flip-flop using NOR latches. Now, substitute that 3 NOR circuit for the 3 input NOR in the flop circuit and see how much goofier it gets.

[One of Many]

Ya know, I had a slight glimmer you might have been pointing to that, but then I thought that if all you had available was a 2 input nor DIP, this is the way it would be done without adding another device to the circuit.

I have come across 8 input and or nand gates. The single output still follows the gates basic logic no matter how many inputs it has.

DC