Review S-R flip-flop Clocked S-R flip-flop Edge-triggered flip-flops D, J-K, T flip-flops

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# Review S-R flip-flopClocked S-R flip-flopEdge-triggered flip-flopsD - PowerPoint PPT Presentation

Review S-R flip-flop Clocked S-R flip-flop Edge-triggered flip-flops D, J-K, T flip-flops S Q R Q’ The S-R Flip-flop (H) (H) The output Q is called the state of the flip-flop S=1, R=0 Sets the state to 1 S=0, R=1 Resets (or Clears) the state to 0 S=0, R=0 is the Hold state

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Presentation Transcript
Review S-R flip-flop
• Clocked S-R flip-flop
• Edge-triggered flip-flops
• D, J-K, T flip-flops

S

Q

R

Q’

The S-R Flip-flop

(H)

(H)

The output Q is called the state of the flip-flop

S=1, R=0 Sets the state to 1

S=0, R=1 Resets (or Clears) the state to 0

S=0, R=0 is the Hold state

S=1, R=1 is not allowed

current state

next state

Truth Tables, Characterisitic Equation

S R q Q

0 0 0 0

0 0 1 1

0 1 0 0

0 1 1 0

1 0 0 1

1 0 1 1

1 1 0 x

1 1 1 x

HOLD

RESET

SET

not allowed

Because the 11 input will not be allowed, the result is a don’t care, and Q = S + R’q

This is the characteristic equation for an S-R flip-flop

S-R Flip-flop outputs

R

S

Q

Q(H) or

Q’ (L)

Q’ (H) or

Q(L)

A Clocked S-R Flip-flop

S

Q

CLK

R

Q’

When CLK = 0, the flip-flop holds

When CLK = 1

It acts like a regular S-R flip-flop

S

R

CLK

Q

Clocked S-R Flip-flop

S=1, R=1, can occur as long as the Clock=0

Edge triggered flip-flops
• For clocked flip-flops, the output reflects the input as long as the clock =1. When the clock=0, the flip-flop is in the hold state.
• For edge-triggered flip-flops, the output only changes at the edge of the clock
• A positive-edge-triggered flip-flop changes state on the low-to-high transition of the clock ( )
• A negative-edge-triggered flip-flop changes state on the high-to-low transition of the clock ( )

S

S

S

Q

Q

Q

R

R

R

Q’

Q’

Q’

Edge-triggered Symbols

A positive edge triggered flip-flop

Negative edge triggered flip-flops

CLK

Edge triggered S-R Flip-flops

S

R

Q

Positive edge triggered flip-flop

Q

Negative edge triggered flip-flop

The D Flip-flop

D

Q

CLK

Q’

When CLK = 0, the flip-flop holds

When CLK = 1 D q Q

0 0 0

0 1 0

1 0 1

1 1 1

Characteristic Equation: Q = D

J

Q

K

Q’

J K q Q

0 0 0 0

0 0 1 1

0 1 0 0

0 1 1 0

1 0 0 1

1 0 1 1

1 1 0 1

1 1 1 0

Hold

Reset

Set

The J-K flip-flop

Characteristic Equation

Q = Jq’ + K’q

Invert

(or complement)

T

Q

J

Q

Q’

K

Q’

The T flip-flop

T

T q Q

0 0 0

0 1 1

1 0 1

1 1 0

Hold

Invert

(or complement)

Characteristic Equation

Q = Tq’ + T’q