Logic Gates

There are four major logic gates used in circuits. They follow the samelogic that you learned in math class at school (if this,then that) except that instead of trues and falsed theirinputs are binary numbers (0s and 1s). The fours gates are the and, nand,or and nor gates. There are several variations on these gates, but allstem from this basic idea. Logic gates are used in timing and countingdevices among other things.

The and gate  requiresthat both inputs are satisfied by 1s for postive voltage output. Any othercombination of 0s and 1s will result in the output being 0 or "ground."

The nand gate  takesthe output of the and gate and replaces it with the inverse. In other words,all the inputs except for the pair of 1s give positive voltage output.

The or gate  requiresthat at least one of the inputs be a 1, for positive voltage output. Thereforethe only pair of inputs that would be grounds are a pair of 0s.

The nor gate  takethe output of the or gate and replaces it with the inverse. The only pairthat now satisfies the input is the pair of zeros.