Flip flop, latch, difference between flip flop and latch,

triggering and clocking, shift

register, its type and application

K-13ME05 Akash Thahrani

• Logic circuits are classified into two groups i. Combinational circuit ii. Sequential circuit• Basic building block of combinational circuit is logic gates, while indeed

the basic building block of Sequential circuit is flip flops• Flip flop has better and greater usage in shift register, counters and

memory devices • Flip flop is a storage device which store one bit data• It has two input and two output labeled as Q and Q’ • Normal and complement • Latch: it is also building block of sequentional circuit, which is constructed

by the pair of, neither, neither crossed, coupled of NOR gate...• It is a digital storage device, serve as temporary buffer memory.

Flip flop

• There are three types of flip flopi. Clocked S-R flip flopii. D flip flopiii. J-K flip flopS-R flip flop: It has two input S and R and two output Q and Q’. In

flip flop output are always opposite, if Q=1 then Q’=0. In wiring diagram of R-S flip flop, there are two NAND

gates.

Types of flip flop

Mode of operation

S R Q Q’ Effect of output

Prohibited 0 0 1 1 Prohibited do not use

Set 0 1 1 0 For setting Q to 1

Reset 1 0 0 1 For setting Q to 0

Hold 1 1 Q Q’ Depend on privious state

Truth table of R-S flip flop

• D stands for delay.• It has only one data input D and a clock signal

(CLK).• Output are labeled as Q & Q’.• Notice that output Q follows input D after one

clock puls (see Qn+1 column).• D flip flop may be formed as clocked signal R-S

flip flop by adding an inverter.

D flip flop:

J-K flip flop

• J-K flip flop act as R-S flip flop except that it does not have a invalid state.

• J & K does not mean any special but J is equivalent to set and K is equivalent to reset.

• R=S=1 state has been replaced with a toggle state.• Toggle means the output will change to the

opposite state (0 to 1 or 1 to 0) after every clock transition.

• The JK is in R-S flip flop with feedback from Q & Q’.

• Flip flop and latch are two basic building blocks of sequentional 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 inputs and correspondingly changes its output, independent of time determined by clocking signal.

Difference between flip flop and latch

•A unique signal called “enable” is provided with latch.•The output changes only when enable signal is active.•No change in output take place when the enable signal is inactive.•Flip flop are edge trigger, while latches are level trigger.

• A trigger is a control signal used to initiate an action.

• In gated latches, the trigger is enable line. Setting the enable high allows the latch to be set or reset.

o There are two forms of trigger:

1.Level trigger (High or low)2.Edge trigger (+ve or –ve going transition)

Triggering and clocking

• Shift registers are type of sequentional logic circuits mainly for storage of digital data. The word shift means the device which shift data right or left. i.e. calculator

• They are a group of flip flop connected in chain so that output from one flip flop becomes the input of next flip flop.

• Most of the register posses no characteristics internal sequence of states.

• All the flip flop are driven by common clock and all are set or reset simultaneously.

Shift Register

• There are four types of shift registers;1) Serial in, Serial out (SISO)2) Serial in, Parallel out (SIPO)3) Parallel in, Serial out (PISO)4) Parallel in, Parallel out (PIPO)Serial in

Serial out

Serial in Parallel out

Parallel in Serial out

Parallel in Parallel out

1 0 1 1 0

1 0 1 1 0

1 0 1 1 0

1 0 1 1 0

• The serial load shift register is constructed from four D flip flop. It is called four bit shift register because it has four place to store data A, B, C, D.

• In table first clear (CLR input to 0) all output A, B, C, D to 00000.

• This output 00000 remains same, while they are await a clock pulse. Pulse the CLK input once the output now will be 1000, again pulse clocking 1100.

Serial load shift register

Line no: Clear Data Clock pulse FF A FF B FF C FF D

1 0 0 0 0 0 0 0

2 1 1 0 0 0 0 0

3 1 1 1 1 0 0 0

4 1 1 2 1 0 0 0

5 1 1 3 1 1 1 0

6 1 0 4 0 1 1 1

7 1 0 5 0 0 1 1

8 1 0 6 0 0 0 1

9 1 0 7 0 0 0 0

10 1 0 8 0 0 0 0

11 1 1 9 1 0 0 0

12 1 0 10 0 1 0 0

13 1 0 11 0 0 1 0

14 1 0 12 0 0 0 1

15 1 0 13 0 0 0 0

Truth table

• The serial load shift register, we studied last has two disadvantages;

• It permits only one bit of information at a time• And it losses all its data out the right side when it

shift right.• But in parallel load shift register given in figure it

permits 4 bit at once, these inputs are data inputs A, B, C, D. This is just like rectangular feature, that would put output data back into so that is not lost.

Parallel load shift register

Line no:

Clear DataA

Data B

DataC

Data D

Clock pulse

FF A FF B FF C FF D

1 1 1 1 1 1 0 1 1 1 02 0 1 1 1 1 0 0 0 0 03 1 1 0 1 1 0 0 1 0 04 1 1 1 1 1 1 0 0 1 05 1 1 1 1 1 2 0 0 0 16 1 1 1 1 1 3 1 0 0 07 1 1 1 1 1 4 0 1 0 08 1 1 1 1 1 5 0 0 1 09 0 1 1 1 1 0 0 0 010 1 1 0 0 1 0 1 1 011 1 1 1 1 1 6 0 0 1 112 1 1 1 1 1 7 1 0 0 113 1 1 1 1 1 8 1 1 0 014 1 1 1 1 1 9 0 1 1 015 1 1 1 1 1 10 0 0 1 1

Truth table

• There are so many applications of shift registersi. To produce time delay,ii. To simplify combinational logiciii. To convert the serial data to parallel data.• Shift register have both parallel and serial

input and outputs.• This is bi directional shift register which allow

shifting to both direction LR or RL.

Application of shift register