Pulse Triggered (Level Triggered or Gated) SR Flip Flop (Latch)
Summary
TLDRThis video explains the working of a pulse-triggered SR flip-flop, also known as a gated SR flip-flop or SR latch. It discusses how the output responds to input changes at specific levels of the enable signal (positive or negative), and illustrates the behavior of the SR latch with a circuit diagram, truth table, and waveform analysis. The video emphasizes the differences between positive and negative level triggering and concludes with the characteristic equation for an SR latch. The next video promises to explore edge-triggered SR flip-flops, highlighting the contrast between level and edge triggering.
Takeaways
- ⚡ Pulse-triggered flip-flops, also known as level-triggered or gated flip-flops/latches, respond to input changes at a specific level of the enable signal.
- 🔌 The SR flip-flop has two main inputs, S (set) and R (reset), along with an enable input (E or G) that controls when the flip-flop is active.
- 🟢 When the enable input is at a positive level, the flip-flop becomes active and reacts to changes in S and R inputs.
- 🔴 If the enable input is zero, the flip-flop ignores changes in S and R, maintaining its current state.
- 🧮 The truth table shows that the SR flip-flop's next state depends on both S and R inputs and the enable signal, determining whether the flip-flop sets, resets, or holds its value.
- 📝 A flip-flop is considered 'set' when S = 1, R = 0, and the output becomes 1, and it is 'reset' when S = 0, R = 1, making the output 0.
- ⛔ When both S and R are 1, the flip-flop state is indeterminate, meaning the output is undefined.
- 🔄 The characteristic equation of the SR latch describes the relationship between present state, next state, and the S and R inputs, forming the basis for predicting its behavior.
- 🌊 The behavior of the gated SR latch can be visualized with timing diagrams that show how the output responds to changes in enable, set, and reset signals over time.
- 🔄 The flip-flop behaves differently under negative level triggering, where it becomes active when the enable input is 0, instead of 1.
Q & A
What is a pulse-triggered SR flip flop?
-A pulse-triggered SR flip flop, also known as a level-triggered or gated SR flip flop, responds to input changes only when there is a positive or negative level on the enable input. The enable input can be referred to as the gate signal, and it controls when the flip flop is active.
What are the inputs of a pulse-triggered SR flip flop?
-The inputs of a pulse-triggered SR flip flop include the Set (S), Reset (R), and Enable (EN) or Gate (G) signals. The flip flop's output depends on the state of these inputs, particularly when the enable signal is at an active level.
What happens when the enable input is 0 in a pulse-triggered SR flip flop?
-When the enable input is 0, the output of the flip flop remains unchanged, regardless of the values of the Set (S) and Reset (R) inputs. The output will follow the previous state.
What is the significance of a positive level-triggered flip flop?
-In a positive level-triggered flip flop, the flip flop only responds to input changes when the enable input is at a positive (high) level. This makes the flip flop active and able to produce output based on the current inputs.
What is the output of a flip flop when S = 0, R = 1, and the enable signal is 1?
-When S = 0, R = 1, and the enable signal is 1, the flip flop will reset, meaning the next state of the output will be 0, indicating the reset state.
What is the output when both S and R are 1 in a pulse-triggered SR flip flop?
-When both S and R are 1 in a pulse-triggered SR flip flop, the output becomes indeterminate or undefined. This is typically avoided in practical use since the flip flop does not produce a clear output in this state.
How does the gated SR flip flop work in relation to enable input timing?
-The gated SR flip flop only responds to input changes when the enable input is 1 (positive level). If the enable input is 0, the flip flop holds its current output. The waveform of the enable signal controls when the flip flop can update its output based on the Set and Reset inputs.
What is the difference between a positive level-triggered and a negative level-triggered SR flip flop?
-A positive level-triggered SR flip flop responds to inputs when the enable signal is at a positive (high) level, while a negative level-triggered SR flip flop only responds when the enable signal is at a negative (low) level. The behavior of the flip flop changes based on the level of the enable input.
What does the characteristic equation of an SR flip flop represent?
-The characteristic equation of an SR flip flop defines the relationship between the next state of the flip flop (Qn+1), the current state (Qn), and the Set (S) and Reset (R) inputs. It is a formula that helps predict the output of the flip flop based on its inputs and current state.
What is the purpose of using a gated SR latch instead of a regular SR latch?
-A gated SR latch includes an additional enable input that controls when the latch can respond to changes in the Set and Reset inputs. This allows for more controlled operation, as the latch only updates its output when the enable signal is active, making it more suitable for synchronous circuits.
Outlines
🔄 Introduction to Pulse-Triggered SR Flip-Flop
This paragraph introduces the concept of a Pulse-Triggered SR Flip-Flop, also known as a Level-Triggered or Gated SR Flip-Flop/Latch. It explains that the flip-flop's output responds to the level of the enable input, which acts as a gate. The flip-flop has two inputs, S (set) and R (reset), and an additional enable or gate input. The behavior of the flip-flop is dependent on the level of the enable input, whether positive or negative. The paragraph also mentions that the flip-flop can be represented as a latch by default but can also be considered as a flip-flop. It concludes by stating that a detailed explanation with a circuit diagram will follow.
📈 Understanding the Operation of SR Flip-Flop with Truth Table
This paragraph delves into the operational details of the SR flip-flop with an emphasis on its truth table. It explains how the flip-flop's output changes based on the inputs S and R, and the level of the enable input. The truth table provided shows the current output (q) and the next output (q+1) of the flip-flop after the enable signal is applied. The paragraph also discusses the concept of positive and negative level triggering, where the flip-flop responds to either the positive or negative level of the enable input. The behavior of the flip-flop is further clarified with examples of how the flip-flop remains unchanged unless the enable input is active (high or low depending on the type).
📊 Waveform Analysis of Gated SR Latch
In this paragraph, the operation of the gated SR latch is explained through waveform analysis. It describes how the flip-flop's output (Q and Q Bar) changes in response to the set (S), reset (R), and enable inputs over time. The paragraph illustrates the flip-flop's behavior when the enable signal is high and when it is low, showing how the flip-flop sets or resets accordingly. The waveforms are used to demonstrate the flip-flop's response to different input combinations, including the indeterminate state when both S and R are high.
🔢 Deriving the Characteristic Equation of SR Latch
The final paragraph focuses on deriving the characteristic equation of the SR latch. It explains that the characteristic equation represents the relationship between the next state of the flip-flop, its present state, and the inputs. The paragraph walks through the process of simplifying the truth table to form the equation, which is expressed as q(n+1) = S + R'q(n). This equation captures the essence of how the flip-flop's next state is determined by the current state and inputs when the enable signal is active. The paragraph also briefly touches on the difference between positive and negative level triggering in SR flip-flops.
Mindmap
Keywords
💡Pulse Triggered
💡SR Flip-Flop
💡Latch
💡Enable Input
💡Positive Level Triggered
💡Negative Level Triggered
💡Truth Table
💡Set
💡Reset
💡Indeterminate State
Highlights
Pulse-triggered SR flip-flop or latch is also known as level-triggered or gated SR flip-flop or latch.
The flip-flop's output responds to input changes only at the positive or negative level of the enable input.
Enable input, also known as gate input, determines the flip-flop's response to input changes.
The SR flip-flop has two inputs, S (set) and R (reset), and an enable or gate input.
The flip-flop's output depends on the level of the enable input or gate signal.
If the output responds to the positive level of the enable input, it is known as positive level-triggered flip-flop or latch.
If the output responds to the negative level of the enable input, it is known as negative level-triggered flip-flop or latch.
The block diagram representation of the SR latch is explained with a gated SR latch.
The SR latch has NAND gates in its circuit.
The truth table of the SR latch is detailed, showing the relationship between present and next outputs.
The flip-flop's output remains unchanged as long as the enable input is zero.
The flip-flop is active only when the enable input is one in positive level-triggered flip-flops.
The flip-flop will reset if S is 0 and R is 1, regardless of the enable input.
The flip-flop will set if S is 1 and R is 0, with the enable input active.
The state of the flip-flop is indeterminate if both S and R are 1.
Waveform analysis demonstrates the flip-flop's response to changes in S, R, and enable inputs over time.
The characteristic equation of the SR latch is derived, relating the next state to the present state and inputs.
The negative level-triggered SR flip-flop is symbolized with a circle indicating negative triggering.
In negative level-triggered flip-flops, the flip-flop is active when the enable signal is zero.
Transcripts
in this video I will discuss about pulse
triggered Sr flip flop or latch so pulse
triggered is also known as level
triggered or also known as gated Sr flip
flop or srf latch so here the name flip
flop
or latch so when there is a pulse
triggering or the level triggering by
default it will be latch but we can also
represent it as flip flop
impulse triggered flip flop output of
the flip flop response to the input
changes only at positive or negative
level of the enable input here the
enable in enable input is nothing but
gate input so sometimes it is also known
as gated flip flop or gated latch so in
Sr flip
so in first triggered Sr flip flop we
have two inputs that is s and r
along with that we have one more input
represented as either by E which
represent enable signal or by G which
represent get signal so here the output
is not only dependent on S standard it
is also dependent on either positive or
negative level of the enable input or
gate signal
if output of the flip flop responds to
the input changes only at positive level
of the enable input then it is known as
positive level triggered flip flop or
latch
similarly if output of the flip flop
responds to the input changes only at
negative level of the enable input then
it is known as negative level triggered
flip flop or latch
now let me explain this in detail with
circuit diagram
so this is the block diagram
representation of Sr latch that is gated
SRH or pulse triggered Sr latch now let
me write it as
R latch
so here we have two inputs that is one
input is s s represents set and R which
is nothing but reset
so here this is the enable input I will
represent it as say en so in place of En
we can also use g g for gate it has two
outputs one is
Q output another output is q1 which is
complement of this Q output
so here this is the circuit of Sr latch
with nand Gates so here this is s input
that is set and we have r that is this
is our input and this one is nothing but
enable input it has two output that is q
and Q Bar so this is Q output and this
will be Q Bar output
so in my Sr Latch video I have clearly
explained how this Sr latch will work
now directly I will write this truth
table
that is
so here en stands for enable input SC
set R is reset q n q n stands for
present output q n plus 1 stands for
next output
the difference between present output
and next output is after applying the
enable signal
the flip flop produce the output that
we'll call it as next output and this
state indicates the status of the flip
flop so in
pulse triggered flip flop as long as
enable input is zero that is if enable
input is zero
irrespective of S and R that is s may be
0 or 1 that is do not care R may be 0 or
1
suppose the present state of the flip
flop is zero
so when enable is 0 the next state of
the flip flop will be zero
similarly if enable input is zero
irrespective of S and R that is s may be
0 or 1 or maybe 0 or 1 suppose the
present state of the flip flop is one in
that case also the next state is same as
the present state that is next state is
same as present State now here we can
say the status of the flip flop as there
is no change in the output that is
present State and next state outputs are
same we can call it as no change
there is no change in the output so here
also there is no change in the output as
I said here we'll consider positive
level triggered so let me let e n is
positive level triggered in that case
when e n is 1 then only flip flop will
be active that is if n is 1
so in all other cases I will consider e
n as 1
so if S and R are
s is 0 and R is 0
that is SC 0 R is 0 suppose present
state of the flip flop is 0 in that case
if s is 0 R is 0 the next state of the
flip flop is
same as present State there is no change
similarly
for S is 0 and R is 0 suppose q n that
is present state is 1 in that case also
next state will be same as present state
so here also there is no change
here also we have
no change
so now let me consider
suppose yes input is 0
R input is 1
if q n there is present state of the
flip flop is 0 in that case here we can
see that s c is 0 that is set equal to 0
and reset is equal to 1 in that case the
flip flop will reset that is next state
of the flip flop is reset reset means
zero the status or state is reset the
flip flop will be in reset state that is
if s is 0 and R is 1 flip flop is reset
means 2N plus 1 is 0 or Q is 0.
similarly
the same thing that is s is 0 and
R is 1 but present state of the flip
flop is say one in that case as I said
here s is 0 R is 1 means it is flip flop
is reset the present state q n is equal
to 1 it indicates that flip flop is in a
set state that is Q equal to 1 means
flip flop is in set state
so the next state of the flip flop will
be zero
so when s is 0 R is 1 when reset is one
flip flop will reset so flip flop is
reset means output is zero here also it
is reset
similarly
suppose s is 1
and R is 0 so flip flop will set
so here s is 1 R is 0 R is 0 and enable
input is one therefore the flip flop
will set so it will be set similarly for
the same state that is let me consider s
equal to 1 r equal to 0 suppose flip
flop is in
set state that is 1 so in that case
when s c is 1 R is 0 suppose the flip
flop is in set state it will follow the
same state in the next state when that
is one itself so here also it is set
suppose s is 1 and R is 1
q n is 0
so in Sr flip flop if S and R are one
that is if both the inputs are 1
and if 2 N is 0 there is present state
of the flip flop is 0 then q n plus 1
will be not defined in both the cases it
will be not defined
we'll call it as indeterminate
here also it is indeterminate
now let me explain the working of this
flip flop that is gated Sr latch with
waveform
so I will consider this signal as set
signal that is s
I will call this signal as set
I will call this signal as say reset
and let me take this as enable input say
this is enable input or gate input so
here we can observe that from here to
here it is 0 enable signal is zero
from here to here it is 1 and from here
to here it is again 0 and from this
period to this period its value is 1
after that its value is 0.
so this is with respect to time
so let me take this as Q output
that is output of the Flip Flop and let
me take this as
Q Bar because flip flop has two outputs
q and Q Bar both are complement of each
other so here
as I said according to according to this
truth table when enable input is 0 flip
flop there is no change in the flip flop
so here that we can observe here
so from this period to this period the
enable signal is zero at in this period
the value of that is
I can show here from here to here the
value of s is 0 here the value of R is 0
that is when s is 0 or R is 0 that is
irrespective of this the flip flop will
follow the same previous value that is q
n plus 1 is same as q n it means that it
will follow
the previous value that is the if we
assume the previous value as 0 the flip
flop will become 0 itself
so from till this period its value will
be 0
so now from here to here that is from
here to here the value of s is 0 value
of R is 0 but enable signal is one here
we can see that enable signal is one so
when enable is 1 s is 0 and R is zero
you both s is 0 and R is 0 there is no
change so no change means the flip flop
will carry the previous value the
previous value was 0 the same thing will
continue so from here to here the same
thing will continue
so now at this moment we can see that s
value is 1 from here to here this value
is 1 but here the R value is 0 the flip
flop is in
enable equal to 1. so here we can see
that s is one R is 0.
so into table we can see s is one R is 0
flip flop will be in set state
here also we can see enable is 1. so
that the flip flop will become set set
means one the flip flop will go higher
output will be high so till from here to
here the output is high
so from here to here I can show here
here to here the output is high
so now from this point to this point s
is 0 and R is 0 when s is 0 and R is 0
and enable is 1 here also enable is one
we can see that s is 0 R is 0 enable is
one there is no change
because there is no change means if the
previous output was Zero the same thing
will be followed if it is 1 same thing
will be followed so here we can see that
the previous one was one
previous output was one same thing will
be carried so it will be 1 itself so
till this point its value is 1.
so at this moment we can see that R is
equal to 1 here but s is equal to zero
so when s is 0 R is 1 here we can see
that enable is one that is when s is 0 R
is 1 and enable is 1
if flip flop is in previous state is 1
it will become 0 if it is 0 it will
become 0 that is it the flip flop will
become reset
that is here the output is 1 it will
become 0 it will be resetted it will be
reset
so now same thing will be carried
so till here the same thing will be
carried
so from here
the enable signal is zero so when enable
signal is zero the previous output will
be carried so from here to here the
state of the output is same that is Zero
edition
here it will be zero itself from here to
here so again here we have one so
whenever there is a e n is equal to 1
then only the flip flop is active so
again at this moment so here we can see
that
s is 0 here R is 0 it will follow the
previous state till here the output of
the flip flop is 0 itself
when it reaches here
the r is 1 s is 0 and enable is 1 it
means s is 0 R is 1 means flip flop will
be reset
so already it is in reset
same thing will be continued again till
this point
till this point same thing will be
continued so at this moment
here s is 0 R is 0 again the same thing
will be continued till this point the
same thing will be continued
so at this moment we can see that s is
equal to 1 R is 0 and enable is 1 so
when s is one R is 0 flip flop will set
the flip flop will go high
and it will be high until this point
till this it will be high so here we can
see that after this the enable signal
will become zero when enable will become
0
the flip flop will carry
there is no change no change means flip
flop will carry the same previous output
so it will remains one
here onwards enable is 0 the flip flop
output should be like this so this is
the Q output so the Q Bar output is
always the complement of Q just draw the
complement of this q that is
from here to here it is 0 so here it
will be 1
so from here to here it is 0
from here to this point it is 0 so
complement is 1 so here it will be 1
can draw like this and here onwards it
will be zero
so this is how the flip flop or gated Sr
latch will work now let me derive the
characteristic equation of Sr latch
characteristics equation of Sr latch
so characteristic equation gives the
relation between next state of the flip
flop present state of the Flip Flop and
yes and our inputs
so here we can see that S and R are the
inputs qn is present state of the flip
flop q n plus 1 is next state of the
flip flop characteristic equation gives
the relation between q n plus 1 with q n
s and r so here we'll consider s r and q
n as a input q n plus 1 as a output
so let me consider
this is yes input here we have R and
q n
so we know that this is 0 0 of cell this
is 0 1 1 0 1 1 this is 0 and this is 1.
so this is cell number 0 1 2 3
4 5 and here we have 6 and 7.
so let me ignore the first
these two inputs that is when en is 0
consider only when n is 1 so here we
have
this is 0 1 4 1 the value is one
and for 4 1 0 0 4 4
value is 1 and for cell number five
value is one so for the cell number one
four five the value of the flip flop is
one
let me write
one four five that is one
four five value of the flip flop is one
and four six and seven value is don't
care
for six and seven value is don't care in
all other cells the value is zero
so let me simplify this so here I can do
1 1 x x can be done one square
here this is required the value of this
is so it covers the row one which is
with respect to yes
so here we have one
so this one and this one can together
make a pair
here the value of this is
here R Bar q n that is R Bar q n so
therefore we can write
q n plus 1 is equal to we have S Plus R
Bar q n
R Bar
q n this is the characteristic equation
for Sr latch or Sr
gated Sr latch that is q n plus 1 equal
to S Plus R Bar q n so this is all about
positive level triggered Sr flip flop
flip flop
so in negative level triggered Sr flip
flop the symbol of the SR latch can be
represented as everything is same for
enable here we supposed to put the
circle that Circle indicates
negative H triggered so through Circle
this circle indicates negative is
triggered or enable signal is low so in
that case here the enable signal when
enable signal is one the flip flop is
not active the flip flop will not
respond and the flip flop will be active
only when enable signal is zero so
everything is same only this enable
signal inputs will be zero
so rest s r u n q n plus 1 and state
will be remains same
thank you for watching in my next video
I will discuss about
Edge triggered Sr flip flop you can come
to know the difference between level
triggered and Edge triggered Sr flip
flop thank you for watching
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