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SEQUENTIAL CIRCUITS

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Two Types of Switching Circuits

• Combinational Circuits– Combinational circuits have only input and output. Output

depends on input.

– Example: AND,OR,NAND,NOR,XOR etc

• Sequential Circuits– Sequential circuits have input, present state, next state and

output. Next state depends upon present state and input. Output depends upon present state and input

– Example: Flip-Flops etc

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FLIP FLOPS AND THEIR APPLICATIONS

1.

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When S = 1, Q+ = 1When R = 1, Q+ = 0When T = 1, State changesWhen any two out of S,R,T equals 1, we have don’t care

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Example 1:

Design a modulo-8 binary -up counter usingT- Flip Flop

Modulo 8 counter :Counts upto 7 . So we need three Flip-flops foreight states

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modulo-8 counter

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modulo-8 counter

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modulo-8 counter

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modulo-8 counter

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Modulo 8 counter :Counts upto 7 . So we need three Flip-flops foreight states

Example 2:

Design a modulo-8 binary -up counter usingT- Flip Flop with input x

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modulo 8 counter with I/p x

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modulo 8 counter with I/p x

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modulo 8 counter with I/p x

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modulo 8 counter with I/p x

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Example 3:

Design a binary decade counter using SR- Flip Flop without input x

Decade Counter:Counts up to 9 . So we need four Flip-Flops

for ten states

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Binary Decade counter

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Binary Decade counter

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Binary Decade counter

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Binary Decade counter

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Binary Decade counter

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Example 4:Design a modulo-8 counter which counts in the

way specified below, use J-K Flip-Flop.

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TRUTH TABLE:

present state next state

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Gray code counter

Y3

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Y2

Gray code counter:

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Y1

Gray code counter:

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Example 5:

Design a T-Flip-Flop using S-R Flip-Flop

Sol:

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T Flip flop using S-R flipflop

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Example 6:

Design a J-K Flip Flop using S-R Flip Flop

Sol:

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J-K Flip Flop using S-R Flip Flop

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Example 7:Design a sequential circuit given below using J-K FlipFlop

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Truth Table:

Present st. Next state o/pI/p

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Design of Seq. Circuit

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Design of Seq. Circuit

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Design of Seq. Circuit

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Design of Seq. Circuit

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Example 8:

Design a binary modulo-5 counter using SRT- Flip Flop with input x

Modulo-5 Counter:Counts up to 4 . So we need three Flip-

Flops for five states

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STATE TABLE

Binary Modulo-5 counter

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Binary Modulo-5 counter

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Binary Modulo-5 counter

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Note: Here S’and C’ stands for the compliment value of the corresponding cells in the S and C K-maps

Binary modulo-5 counter

Assume T’ = So S’ and C’ comes out to be

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Binary Modulo-5 counter

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Assume T’ = So S’ and C’ comes out to be

Binary modulo-5 counter

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Binary modulo-5 counter

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Assume T’ = 1So S’ and C’ comes out to be0 and 0

Binary modulo-5 counter

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G = 0 Q+ does not respondG = 1 Q+ responds

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T-G Flip Flop Application Equation

This is the Application Equation of the T-G Flip-Flop

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Example 9:

Design T2 and G2 for a modulo-5 binary up counter

Modulo-5 counter:Counts up to 4 . So we need three Flip-

Flops for five states

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STATE TABLEModulo 5 binary upcounter

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Modulo 5 binary upcounter

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Modulo 5 binary upcounter

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Modulo 5 binary upcounter

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Modulo 5 binary upcounter

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Example 10:

Design an Octal upcounter(Binary counter) using S-C Flip-Flop using Tabular Method

Octal up counter:Counts up to 7 . So we need three Flip-

Flops for seven states

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STATE TABLE

Octal up counter

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Octal up counter

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Octal up counter

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Octal up counter

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RULES TO DERIVE EXCITATION FUNCTION

• T- Flip-Flop

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• S-C Flip Flop

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• J-K Flip Flop

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• T-G Flip Flop

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• S-C-T Flip Flop

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Summary of Rules for all Flip-Flops

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MODIFIED RULES FOR THE FLIP-FLOPS

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questions ???