Flip-Flops

RS Flip-flop

S

R

OutputsInputs

X

X

RS Flip-flop - definition

Inputs Output

S R

0 0 Unchanged

1 0

0 1

1 1 Not allowed

01 XX

10 XX

RS Flip-flop waveforms

01 XX 01 XX

Types of flip-flops:a) dynamicb) synchronized

Example

Example continuation

RS flip-flop formed by cross-coupling NOR gates

RS flip-flop formed by cross-coupling NAND gates

Transfer circuit

RS latch

D latch

Shift register

The progression of states by the counter

X3 X2 X1

0 0 0

0 0 1

0 1 0

0 1 1

1 0 0

1 0 1

1 1 0

1 1 1

0 0 0

… … …

Example: Binary counter

Example: Gated-clock binary counter

JK flip-flop

Example: Binary counter

made with JK flip-flops

Example: Up-down counter

Integrated circuits

Counter design:Design rule for RS flip-flops

The present state

The next state S R

0 0 0 d

1 1 d 0

0 1 1 0

1 0 0 1

Counter design: Exercise (RS version)

Design a counter using three RS Flip-Flops

to sequence as follows

A B C

0 0 0

1 1 1

1 0 1

1 1 0

0 0 1

0 1 0

0 0 0

1 1 1

1 0 1

... ... ...

Solution: (RS version)

Solution: Counter with RS flip-flops

AS

R

BS

R

S

R

C

Counter design: Design rule for JK flip-flops

The present state

The next state J K

0 0 0 d

1 1 d 0

0 1 1 d

1 0 d 1

Counter design: Exercise (JK version)

Design a counter using three JK Flip-Flopsto sequence as follows

A B C

0 0 0

1 1 1

1 0 1

1 1 0

0 0 1

0 1 0

0 0 0

1 1 1

1 0 1

... ... ...

Solution: (JK version)Counter with JK flip-flops