2. Sequential Circuits
The output of circuit depends on the
previous output and the present input.
The input must follow a specific sequence to
produce a required output.
In order to follow a sequence of input the
circuits must contain some form of memory
to retain knowledge of those inputs.
This memory are obtained by feedback
connections.
Most sequential systems are based on a small
number of simple sequential circuit elements
known as flip flops.
3. Flip-flop (Sequential Circuits)
What is Flip flop?
It is a Sequential circuits/an electronics circuit which has two stable states
and thereby is capable of storing as one bit of data, bit 1 or bit 0.
4. Introduction – flip-flop
They are 1(HIGH) or 0 (LOW).
Whenever we refer to the state of flip-flop, we
refer to the state of its normal output(Q).
More complicated flip flop use a clock as the
control input. These clocked flip-flops are used
whenever the input and output signals must occur
within a particular sequence.
Normal output
Inverted Output
Inputs
They have two stable conditions and
can be switched from one to the other
by appropriate inputs. These stable
conditions are usually called the states
of the circuit.
Q
𝑄
5. Introduction: Types of Flip Flop
1. S-R latch
2. Clocked S-R Flip-Flop
3. J-K Flip Flop
4. D Flip Flop
5. T Flip Flop
6. Master-Slave J-K Flip Flop
6. Difference between flip flop and latch
Flip flop and latch are two basic building blocks of sequential circuit but
there is suitable difference between the two is;
A flip flop continuously checks its inputs and corresponding changes its
output only at times determined by clocking the signal.
Where as latch is a device which continuously checks all its input and
correspondingly changes its output, independent of time determined by
clocking signal.
7. S-R Latch
The most basic sequential circuit is called
SR latch.
The basic SR latch is an asynchronous
device.
In asynchronous device, the outputs is
immediately changed anytime one or more
of the inputs change just as an
combinational logic circuits.
It does not operate in step with a clock or
timing.
S
R
Q
𝑄
8. S-R Latch
The SR latch has two inputs, SET(S) and
RESET(R).
The SR latch has two outputs Q and 𝑸.
The Q output is considered the normal
output and is the one most used.
The output 𝑸 is simply the compliment of
output 𝑸.
S R Q 𝑸 STATUS
0 0 1 1 INVALID
0 1 1 0 SET
1 0 0 1 RESET
1 1 Q 𝑄 HOLD
(NO
CHANGE)
10. Clocked S-R Flip Flop
Additional clock input is added to
change the SR latch from an element
used in asynchronous sequential circuits
to one, which can be used in
synchronous circuits.
Its means that the flip flop can change
the output states only when clock signal
make a transition.
S
R
CLK
Q
𝑄
11. Clocked S-R Flip Flop
CLOCK S R Q 𝑸 STATUS
1 0 0 Q 𝑄 HOLD
(NO
CHANGE)
1 0 1 0 1 RESET
1 1 0 1 0 SET
1 1 1 0 0 INVALID
Truth Table: Logic Circuit:
13. JK Flip Flop – Symbol
Another type of Flip flop is JK
FLIP FLOP.
It differs from the SR flip flops
when J=K=1 condition is not
indeterminate but it is defined to
give a very useful changeover
(toggle) action.
Toggle means that Q and 𝑸 will
switch to their opposite states.
The JK flip flop has clock input
and two control inputs J and K.
Operation of JK flip flop is
completely described by truth
table in figure:
J
K
CLK
Q
𝑄
14. JK Flip Flop – Truth Table And Logic circuit
CLOCK J K Q 𝑸 STATUS
1 0 0 Q 𝑄 HOLD
(NO
CHANGE)
1 0 1 0 1 RESET
1 1 0 1 0 SET
1 1 1 𝑄 Q TOGGLE
Truth Table: Logic Circuit:
Race around condition: As we know that during high clock whenever applied input
changes the output also changes. But in JK flip flop when J=K=1 ,without any change
in the input the output changes , this condition is called as race around condition.
16. D Flip flop
Also known as Data Flip flop.
Can be constructed from SR
flip flop or JK flip flop by
addition of an inverter.
Inverter is connected so that
the R input is always the
inverse of S (or J input is
always complementary of K).
The D flip flop will act as a
storage element for a single
binary digit(bit).
17. D Flip Flop- Logic circuit – Truth Table
D CLK Q 𝑸 STATUS
0 1 0 1 RESET
1 1 1 0 SET
Logic Circuit:
Truth Table:
18. T Flip Flop
The T Flip flop has only
the TOGGLE and HOLD
operation.
If Toggle mode operation
, the output will toggle
from 1 to 0 or vice versa. T CLK Q 𝑸 STATUS
0 1 Q 𝑄 HOLD
1 1 𝑄 Q TOGGLE
Truth Table:
Logic Symbol:
19. Master Slave JK Flip-Flop
Master Slave JK flip flop is designed
using two separate flip flops. Out of
these, one acts as a MASTER and
other as a SLAVE.
The output of master JK flip flop is
fed to the input of the slave JK flip
flop. The output of slave JK flip flop is
given as a feedback to the input of
master JK flip flop.
The clock pulse is given to the master
JK flip flop and it is sent through a
NOT gate and thus inverted before
passing it to the slave JK flip flop.
20. Flip Flop : Application
REGISTERS
FREQUENCY DIVIDERS
DIGITAL COUNTERS
21. Conclusion
Flip flop is a basic memory element which store
one bit at a time and have two states set and
reset.
There are different types of flip flop S-R, J-K, D, T,
Master Slave.
The number of inputs and the way inputs are
given define the type of flip flop.
22. References
Salivahana, S. Arivazhagan, S. 2012. Digital Circuits and Design: Flip-
flops. Vikas
Publishing House Pvt Ltd, New Delhi.
DAEnotes. Flip-flops. http://www.daenotes.com/electronics/digital-
electronics/flip-flops-types-applications-woking
Wikipedia. Flip-flops (electronics). https://en.wikipedia.org/wiki/Flip-
flop_(electronics)
