One thing that is really common in computers are sequences. Things happen, one after the other, in an ordered, regular, pattern.
Sequences are formed in computers when a binary number is decoded onto a set of lines. Each of the output lines is activated, in turn, when the binary number on the inputs lines counts up.
Try it in the simulator to see what we mean. Press the up arrow over the right hand digit in the double digit input on the left of the screen and watch the lights go off in sequence.
We call this an "active low" output because... well actually it's because we were too lazy to invert the output of each NAND gate with an NAND-as-NOT.
Can you modify this circuit to have "active high" outputs? Warning: You won't be able to save your work here; it's just to learn how to do it.
bit chip #
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<A HREF="http://www.piclist.com/techref/logic/2to4ndecoder.htm"> Digital Logic Tutorial, 2 bit to 4 line decoder with active low output</A>
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