This presentation discusses latches and counters. It defines a latch as an electronic circuit with two inputs and one output. There are four main types of latches: SR, D, JK, and T. SR latches can be made from NOR gates and have two states, set and reset. Counters are digital devices that cycle through predefined states based on input pulses. There are two main types of counters: synchronous counters which use a clock signal to change states, and asynchronous counters where states change independently of a clock. Examples of practical uses of counters include appliances like microwaves and washing machines that count time.

1. Presentation on :
Latch and Counter.

2. Submitted By
Delowar Hossain
Dolon
ID: 00817206031
Departmet of CSE
Pundra University of
Science & Technology
Submitted TO
Tahrima Islam
Lecturer
Department of CSE
Pundra University of
Science & Technology

3. What is Latch?
 A latch is an electronic logic circuit that has two
inputs and one output. One of the inputs is called
the SET input; the other is called the RESET input.

4. Working States of Latch circuit:
 Latch circuits can work in two states :
 In case of Active – High latch circuits, normally both
the inputs are low. The circuit is triggered by a
momentary high on either of the inputs.
 In case of Active – Low latch circuits, normally both
the inputs are high. The circuit is triggered by a
momentary low on either of the inputs.

5. Types of latches
 There are four types of latches:
 SR Latch
 D Latch
 JK Latch
 T Latch

6. SR Latch:
 A set/ reset latch is an asynchronous device, which relies on
the state of the S&R inputs. This latch can be made from
NOR gates. The latch has memory and the output depends
on the state of the latch. Therefore, the output at nth
instant denoted by Qn is dependent on the output at (n-1)th
instant, denoted by (Qn-1).

7. SR Latch Continue..
 Note that when the SR=11 state, then both the
outputs are 0, which seems absurd. Thus, the state
SR=11 is said to be “not allowed”. The latch (SR) ̅ is a
similar latch to SR which can be made from the
NAND gates.

8. What is Counter ?
 A counter is a digital sequential logic device that will
go through a certain predefined states (for example
counting up or down) based on the application of the
input pulses.
 They are utilized in almost all computers and digital
electronics systems

9. Types of counters
 There are two types of counters available for
digital circuits, they are:
 Synchronous counters.
 Asynchronous counters.

10. Synchronous counters:
 The counters which use clock signal to change their
transition are called “Synchronous counters”. This
means the synchronous counters depends on their
clock input to change state values. All flip flops in the
synchronous counters are triggered by same clock
signal.

11. Asynchronous counters:
 The counters in which the change in transition
doesn’t depend upon the clock signal input is known
as “Asynchronous counters”. In these counters, the
first flip flop is connected to the external clock signal,
and the rest are clocked by the state outputs (Q & Q’)
of the previous flip flop.

12. Practical example of counter:
 We use counters in many applications:
 In our kitchen appliances, we use microwave ovens. In that we
set some temperature to heat the food item kept in it. Internally the
counter calculates the increase or decrease in temperature and time.
If it reaches the pre-set temperature, then it prevents from further
heating and spoiling of that food item.
 Washing machines: We use counters in washing machines also.
Similar to the counting operation in microwave oven, the counter in
washing machine counts the time which we set it to operate.
 In both microwave oven and washing machine, we set the
device to particular time, and it starts decreasing for every second.
When the value of counter becomes zero, it activates the switch ON
/ OFF. Thus the operation of the device is controlled by counters.

13. Applications of counters:
 Frequency counters
 Digital clocks
 Analog to digital convertors.
 With some changes in their design, counters can be used as
frequency divider circuits. The frequency divider circuit is that
which divides the input frequency exactly by ‘2’.
 In time measurement. That means calculating time in timers
such as electronic devices like ovens and washing machines.
 We can design digital triangular wave generator by using
counters.
 There are many other type of counters rather than
synchronous and asynchronous counters, such as Decade
counter, Binary counter, Ring counter, Johnson counter, Up /
Down counter etc.

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