SEQUENTIAL CIRCUITS USING TTL 74XX ICS

• Flip Flops (IC 7474, IC 7473), • Shift Registers• Universal Shift Register(IC 74194)• 4- bit asynchronous binary counter(IC 7493).

Flip Flops (IC 7474, IC 7473)Difference between Latch and Flip-flop• Latches are controlled by Enable signal and they are Level triggered, either positive or

negative level triggered. Flip-flops use Pulse or Clock and it is Edge triggered.• In Latches, output state is free to change according to input values, when active level is

maintained at Enable input. In Flip-flops, output responds to the changes in input only at positive or

negative edge of clock pulse at the clock input.

• FLIP-FLOP:Flip-flops are synchronous bistable devices, also known as bistable

multivibrator.Synchronous means output changes state only at a specified point on a

triggering input called Clock(CLK), which is designated as a control input.

• Types:1. S-R Flip flop2. J-K Flip flop3. D Flip flop4. T Flip flop

Edge Triggered S-R Flip flopSymbol

Truth Table

Wave forms

Edge Triggered J-K Flip flopSymbol

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Wave forms

Edge Triggered D Flip flop

Symbol Truth Table

Wave forms

74AHC74-Dual D Flip-flopPin Diagram

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7473-Dual J-K Flip flopPin Diagram

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Flip-Flop Applications

1) Parallel Data storage:Several bits of data from parallel lines simultaneously is stored in a group of

flip-flops.

2) Frequency Division:flip-flop is used to divide(reduce) the frequency of a periodic waveform.When a pulse waveform is applied to clock input of a J-K flip-flop that is

connected to toggle (J=K=1), Q output is a square wave with one-half the frequency of the clock input.

So, a single flip-flop can be applied as a divide-by-2 device.

3) Counting:Flip-flops are used in digital counters.

SHIFT REGISTERS

• Shift registers consist of an arrangement of flip-flops which are used for storage and transfer of data.

• A Register, unlike counter has no specified sequence of states.

• A Register is used for storing and shifting data (1s and 0s) entered into it from an external source.

• DOES TWO FUNCTIONS– DATA STORAGE [DONE BY FLIP-FLOPS]– DATA MOVEMENT[LEFT, RIGHT AND DOWN]

FLIP FLOP AS A STORAGE DEVICE

DATA MOVEMENT IN SHIFT REGISTERS

CLASSIFICATION OF SHIFT REGISTERS

• SERIAL IN/SERIAL OUT SHIFT REGISTER

• SERIAL IN/ PARALLEL OUT SHIFT REGISTER

• PARALLEL IN/ SERIAL OUT SHIFT REGISTER

• PARALLEL IN/ PARALLEL OUT SHIFT REGISTER

SERIAL IN / SERIAL OUT SHIFT REGISTER

SERIAL IN /PARALLEL OUTSHIFT REGISTER

PARALLEL IN / SERIAL OUTSHIFT REGISTER

PARALLEL IN/ PARALLEL OUT SHIFT REGISTER

Universal Shift Register(IC 74HC194)Pin Diagram

Logic Diagram

Truth table

Shift Register-Applications1) Time DelaySerial in/Serial out shift register is used to provide a time delay from input to output.8-bit serial in/serial out shift register is used with a clock frequency of 1MHz to achieve

a time delay (td) of 8µs (8X1µs).

Example• Determine the amount of time delay between the serial input and each

output in below fig. Show with timing diagram

Sol: Clock period is 2µs.Thus, the time delay can be increased or decreased in 2µs. increments from a minimum of 2µs to a maximum of 16µs

2) Serial to parallel data converterSerial data transmission from one digital system to another is commonly used to

reduce the number of wires in the transmission line.A computer or microprocessor based system commonly requires incoming data to

be in parallel format, thus the requirement for serial to parallel conversion.

Serial data format

3) Universal Asynchronous Receiver Transmitter (UART)Computers and microprocessor-based system send and receive data in a

parallel format. These systems must communicate with external devices that send and/or receive serial data. So, an interfacing device is used to do these conversions, which is called as UART.

Counters• Flip-flops can be connected together to perform counting operations, such

a group of flip-flops is called as counter.• Types:1. Asynchronous counters2. Synchronous counters.

• Asynchronous counter:It is also called as Ripple counter.In this, first flip-flop is clocked by the external clock pulse and then each

successive flip-flop is clocked by the output of preceding flip-flop.

• Synchronous counter:In this, clock input is connected to all of the flip-flops so that they are clocked

simultaneously.

Asynchronous counter1) 2-bit asynchronous binary counter

2) 3-bit Asynchronous counter

3)4- bit asynchronous binary counter(IC 7493)

Logic Diagram

A gated reset inputs, Ro(1) and R0(2).When Ro(1) and R0(2)=HIGH, counter is reset to 0000 state

CLR

CLR

Pin Diagram

Truth table

IC 74LS93A