Shift Register (PISO Mode) Video Lecture | Digital Electronics - Electrical Engineering (EE)

in this lecture I will teach you
parallel input serial output mode of
shift register it is a very easy and
important topic at the same time in this
mode the bits are entered in parallel or
you can say simultaneously we have four
bits b0 b1 b2 and b3 and we need to
enter them in parallel manner one very
important thing that you can see in this
circuit is that the output of the first
flip-flop that is q0 is connected to the
input of the next flip-flop that is d 1
yr combinational circuit in this
combinational circuit we have 2n gates
and one our gate the same combinational
circuit is used for the flip-flop number
two and flip-flop number three and we
will see the working of this
combinational circuit in a minute there
are two modes in which this circuit can
walk the first one the first one is the
load mode is the load mode and the
second one is the shift mode is the
shift mode and then if you see the
heading it says parallel input serial
output mode so we have two aims the
first one is the parallel input and the
second one is the serial output so the
first am we will achieve from this first
more that is the load mode by the load
mode we have the parallel input of the
data in which we will enter the data or
load the data in each of this flip-flop
simultaneously flip-flop number 0 will
have be 0 flip-flop number one will have
be one flip-flop number two will have b2
and flip-flop number three will have b3
all these four bits are stored in the
respective flip-flops during this load
mode so let's see how we can have this
load mode for this you need this input
that is shifts last load compliment and
I have used the load compliment here
because we have loading when the input
is low and this shows that it is active
low signal so when it is low it means
when it is 0 here I have a 1 because of
this not gate and here I have a zero so
let's see what are the inputs to the
different n gates that we have you
for the end gate number one the first
input will be 0 that you can see from
here for the end gate number two we have
the first input as one similarly for 3
we have 0 for 4 we have 15 we have 0 and
6 we have a 1 and the another input for
the and gate number one is q0 so we have
we have output as zero because Q zero
and zero will give us zero whereas for
the end gate number to the another input
is B 1 and 1 and B 1 will give us be one
similarly we have 0 here b2 here 0 here
and b3 as the output of the and gate
number six now we have or gate and 0 or
B 10 RB 1 is simply equal to b1 so we
have b1 as the input to the flip-flop
number 1 similarly B to as the input to
flip flop number 2 and B 3 as the input
to flip-flop number three so you can see
that we have B 0 is stored in flip-flop
number 0 B 1 stored in flip-flop number
1 B 2 in second flip-flop be three in
third flip-flop so it is a very easy
operation the load mode we have done and
the data is now stored in the flip-flops
what we want next we want the cereal
movement of the data we want the data to
go from flip-flop number 0 to flip-flop
number one in the same way from one to
two and then two to three and the data
is stored in the flip-flop number three
we want as the output so this is what we
want and this is our second aim and it
can be achieved by the shift mode and
during the shift mode we just change
this 0 we just change this 0 to 1 to 1
and because of this we will have 0 here
one at this point and you have to switch
the inputs to your n gate also so we
have one as the first input to gate
number one in the same way we have one
for the gate number three and five and
zero for the gate number two
four and six because of this we have
some changes let's see what they are
first let me drop this down so that we
have some space to write down the
changed outputs okay and for the gate
number one for the end gate number one
you can see the another input is q0 and
the first input is 1 so Q 0 and 1 will
give us q0 so we have q0 and the gate
number two will have output is 0 so this
or gate will give us q0 now it is very
simple to understand that for this
combinational circuit also we have q1
and here we have q2 so you can see that
the data is stored in the flip-flop
number 0 is now shifted to flip-flop
number one q0 was the output and now
this output Q 0 is acting as the input
to d1 so whatever be the value of Q 0 we
have it in the flip-flop number one in
the same way q1 is acting as input to d2
q2 is acting as the input to d3 and
whatever be the value stored in the
third flip-flop is now out so we have q3
as the output and let us take one
example let's take some random bits and
let's see how it moves if we have 10 11
so let's see what we have in that case
for the first mode when the loading of
this shift register is done this one is
stored in the flip-flop number 0 this 0
will be stored to flip-flop number one
this one will store here and this one
will be stored in the last flip flop so
we have 10 11 the parallel storing of
the data is done here and when we have
the shift mode when we change this input
to one there is shifting of data and we
have output as one because one was the
value stored in the flip-flop number
three this one will now be shifted here
and this 0 will now shift it to
flip-flop number two so this one will
now become 0 and this one is shifted to
flip-flop number one so we have one here
so you can see the data is first entered
in
parallel manner we had 10 11 then it is
shifted then it is shifted and we have
one as the output this one is shifted to
flip-flop number three this zero is
shifted to flip-flop number two and this
one is then shifted to flip-flop number
one so this is how the shift register in
parallel input serial output mode works
I hope it is clear to you because you
have already studied the rest of the
three modes that are serial input serial
output parallel input parallel output
serial input parallel output and now we
have also completed the parallel input
serial output mode so there are two
topics still left in the shift register
the first one is the bidirectional shift
register and the next one is the
universal shift register in the next
presentation we will study the
bidirectional shift register so see you
in the next one