1. D Flip-Flops Objectives
Explain the operation of D flip-flops
Understand how reset and preset inputs can be added to any flip-flop
Generate the next state equations and state tables for all types of flip-flops
ECEn 224 Winter 2002
February 15, 2002

2. Set to the state of the D input on clock transition
D Flip-Flops
Set to the state of the D input on clock transition CK Q’
denotes a clock input
denotes transition on
high to low
Flip
Flop Q D
ECEn 224 Winter 2002
February 15, 2002

3. Set to the state of the D input on clock transition
D Flip-Flops
Set to the state of the D input on clock transition CK Q’
Flip
Flop Q D
Q+ = D
ECEn 224 Winter 2002
February 15, 2002

4. D Flip-Flops D Q Clock ECEn 224 Winter 2002 Q’ Q D time CK Flip Flop
February 15, 2002

5. D Flip-Flops (Typical)
ECEn 224 Winter 2002
February 15, 2002

6. D Flip-Flop P P’ Q Q’ Clock ECEn 224 Winter 2002 time D=0 1 1 1 1 11 1 1 1 1
= 0
time
Clock P P’ Q Q’
ECEn 224 Winter 2002
February 15, 2002

7. D Flip-Flop P P’ Q Q’ Clock ECEn 224 Winter 2002 time D=0 1 1 1 1 11 1 1 1 1
01
time
Clock P P’ Q Q’
ECEn 224 Winter 2002
February 15, 2002

8. D Flip-Flop P P’ Q Q’ Clock ECEn 224 Winter 2002 time D=0 1 10 01 11
10
01 1 1 1
01
time
Clock P P’ Q Q’
ECEn 224 Winter 2002
February 15, 2002

9. D Flip-Flop P P’ Q Q’ Clock ECEn 224 Winter 2002 time D=0 1 10 01 11
10
01 1
10
10 1
time
Clock P P’ Q Q’
ECEn 224 Winter 2002
February 15, 2002

10. D Flip-Flop P P’ Q Q’ Clock ECEn 224 Winter 2002 time D=0 1 1 1 10 11
01 1 1
10
10 1
time
Clock P P’ Q Q’
ECEn 224 Winter 2002
February 15, 2002

11. D Flip-Flop P P’ Q Q’ Clock ECEn 224 Winter 2002 time D=0 1 1 1 1 011
01 1 1 1
time
Clock P P’ Q Q’
ECEn 224 Winter 2002
February 15, 2002

12. D Flip-Flop P P’ Q Q’ Clock ECEn 224 Winter 2002 time D=0 1 1 1 1 11 1 1 1 1
time
Clock P P’ Q Q’
ECEn 224 Winter 2002
February 15, 2002

13. D Flip-Flop P P’ Q Q’ Clock ECEn 224 Winter 2002 time D=0 1 1 1 1 101 1 1 1
10
time
Clock P P’ Q Q’
ECEn 224 Winter 2002
February 15, 2002

14. D Flip-Flop P P’ Q Q’ Clock ECEn 224 Winter 2002 time D=0 1 1 01 11 1
01 1
10
10
time
Clock P P’ Q Q’
ECEn 224 Winter 2002
February 15, 2002

15. D Flip-Flop P P’ Q Q’ Clock ECEn 224 Winter 2002 time D=0 01 1 1 011 1
01 1
10
time
Clock P P’ Q Q’
ECEn 224 Winter 2002
February 15, 2002

16. D Flip-Flop P P’ Q Q’ Clock ECEn 224 Winter 2002 time D=0 01 10 1 11 1 1
time
Clock P P’ Q Q’
ECEn 224 Winter 2002
February 15, 2002

17. D Flip-Flop P P’ Q Q’ Clock ECEn 224 Winter 2002 time D=0 1 10 1 1 11 1 1
01
time
Clock P P’ Q Q’
ECEn 224 Winter 2002
February 15, 2002

18. D Flip-Flop P P’ Q Q’ Clock ECEn 224 Winter 2002 time D=0 1 1 1 1 011 1 1
01
time
Clock P P’ Q Q’
ECEn 224 Winter 2002
February 15, 2002

19. D Flip-Flop P P’ Q Q’ Clock ECEn 224 Winter 2002 time D=0 1 1 1 1 11 1 1 1
time
Clock P P’ Q Q’
ECEn 224 Winter 2002
February 15, 2002

20. D Flip-Flop with Reset Input
A reset or clear input is added to many flip-flops for convenience
This overrides other inputs and forces Q to 0
indicates that the reset is active low (reset on CLR = 0) Q’ Q
Clear
CLR CK D
ECEn 224 Winter 2002
February 15, 2002

21. J-K Flip-Flop with Reset and Preset
A preset line is added to force a flip-flops to Q = 1
This overrides other inputs
Clear and preset should not be active at the same time Q’ Q
This J-K flip-flop
operates normally
CLR = 1 and PRE = 0
Clear
CLR
PRE CK K J
ECEn 224 Winter 2002
February 15, 2002

22. Flip-Flop Registers Flip-flops are grouped to form data registers
Clear and preset are for designer convenience in initializing registers
Data Out
Q 1
Q 2
Q 3
Q 4 Q’ Q Q’ Q Q’ Q Q’ Q
CLR
CLR
CLR
CLR CK CK CK CK D D D D
Clock
Clear
D 1
D 2
Data In
D 3
D 4
ECEn 224 Winter 2002
February 15, 2002

23. Characteristic Equations
Set-Reset Trigger J-K D
Q+ = D
Q+ = T  Q
Q+ = TQ’ + Q’T
Q+ = JQ’ + K’Q
Q+ = S + R’Q
(SR = 0)
§ Inputs not allowed
ECEn 224 Winter 2002
February 15, 2002

24. Summary Explain the operation of D flip-flops
Understand how reset and preset inputs can be added to any flip-flop
Generate the next state equations and state tables for all types of flip-flops
ECEn 224 Winter 2002
February 15, 2002