8 Bit Adder Video Lecture | Digital Electronics - Electrical Engineering (EE)

we're gonna take a quick programming
quiz on branch coverage the quiz is
going to involve some Python code that
simulates some adders and that is our
very simple hardware modules that
perform addition here I'm just going to
draw a 1-bit adder to show you how it
works the code that you're going to test
is going to be a cascading series of
eight of these so the way the adder
works is it takes two inputs a and B and
a and B are bits so they're valued in
either 0 or 1 and a Python we're gonna
represent the 1 bit is true and the 0
bit is false so we're gonna use boolean
logic to implement this and there's a
carry bit coming in the output is a
single bit sum of a and B plus a carry
bit out the function implemented by the
adder can be described like this the sum
is the a input exclusive Ord with the B
input exclusive or with a C input and to
do an exclusive or on to billions in
Python we could simply use the not
equals operator the carryout is going to
be equal to a logically ended with B or
the carry end bit and a exclusive o'red
with B and so the Antenor operators in
Python are of course logical and a nor
we have here is a couple of boolean
equations that together implement a full
1 bit adder and if we change these
adders together we can build up
something extremely exciting like an
actual adder the corresponds to the add
instruction that you would find in an
instruction set for a real computer so
now let's look at the code so here I
have some Python code implementing an
8-bit adder so what you can see is it
takes a 0 through a 7 that is to say
eight bits of input the constitute parts
of a where a 0 is the low order bit and
a 7 as a highest bit then B 0 through b7
indicate the bits of the second input
where again B 0 is the lowest order bit
of B and B 7 at the highest and it takes
an initial carry in bit the chain of
logic here is a cascading series of full
adders for the individual bits and as
you can see it's a little bit long and
so now your problem for this API quiz is
to come up with a series of calls to
this 8-bit add function which get 100%
branch coverage and let me give you a
couple of hints so first of all the way
to approach this is probably to think
about how you would test an actual adder
most likely if we're testing an adder
that is to say let's say this code is
part of some sort of a circuit
simulation and we want to test the
validity of our circuit we pass it
actual numbers and so how do you pass it
actual numbers well you can write in
some little support functions for
yourself that take integers and convert
them into the bit format so that's
probably how I would test this and
that's certainly not the only way
you probably don't want to do is treat
this as a black box and so what I'm
deliberately doing here is giving you a
function it's going to be difficult test
if you don't understand its logic at all
so what you need to do is think of this
as an adder and then it really becomes
fairly easy to test