Digital Logic - Decoders
This is one of a series of videos where I cover concepts relating to digital electronics. In this video I talk about decoders, how they are made, and how you can use them
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Video Transcript
hi I'm Jack Buffington for robot
brigade.com this is another video in my
series of videos about digital logic and
in this one I'm going to talk about
decoders now what is a decoder a decoder
is something that takes n inputs and
selects one of one of two to the N
outputs
so you could have a uh two input
decoder and it would select one of four
outputs or you could have a three input
decoder and it would select one of
eight eight
outputs all right let's take a look at
how these work
internally
inside the decoder for every input and
I'm going to draw a uh two input
decoder so actually I'm going to call
this a z and A1 so this is the least
significant bit coming in and this is
your most significant bit first thing
I'm going to do is I'm just going to
have an inverted and a non-inverted
input and and this isn't the most
efficient way to draw it but it's how
I'm going to do it and it should be
pretty
clear all right a decoder is really just
a bunch of and Gates so if I am looking
to decode the value
zero uh where a is zero and A1 is zero
I'm just going to look for a bar uh A1
bar a z
bar okay and if I'm going to decode the
value one that would be a one coming in
here and a zero coming in
here
so got that one and if I'm going to
decode two this one needs to be high
this one low so I'm taking this
one and and this one and finally for
three they both need to be high and so
I'm going to take this one and this one
now there's one other input that you'll
often find on a decoder and that is at
least one enable
input and so if I have enable here if I
have it low then none of these should
ever ever uh go high no matter what
