1. Sequential logic circuits have memory and their outputs depend on both their inputs and present state. They are synchronized by a periodic clock signal. 2. An SR flip-flop is a basic type of sequential circuit that can be constructed using two NOR gates. Edge-triggered flip-flops only change state when the clock signal changes. 3. There are different types of flip-flops like D, JK, and T flip-flops that are used to build sequential circuits. Their behavior and output can be analyzed using state tables and state diagrams that show the unique circuit configurations and transitions between states.

1. Flip Flops
prepared by : Eng. Rania Elsadig
Sudan University of science and
Technology
College of Engineering
Biomedical Engineering Department
Digital Design II
Third year

2. Clock Signal
Sequential logic circuits have memory
Output is a function of input and present state
Sequential circuits are synchronized by a periodic “clock” signal

3. SR Flip Flop
SR (set-reset) flip-flop based on two nor gates

4. SR Flip Flop

5. Edge triggered flip-flop changes only
when the clock C changes
Edge Triggered Flip Flop

6. Exercise
For a given S and R inputs to SR flip-flop,
sketch the output signal Q
Q
t

7. Exercise

8. Positive Edge Triggered D Flip Flop
Positive-edge triggered flip-flop changes only
on the rising edge of the clock C

9. Positive Edge Triggered D Flip Flop Cont.

10. Exercise
The input D to a positive-edge triggered flip-flop is shown
Find the output signal Q
Q
t

11. Exercise

12. Positive Edge Triggered JK Flip Flop

13. Positive Edge Triggered JK Flip Flop Cont.

14. T ( Toggle) Flip Flop

15. +
T ( Toggle) Flip Flop Cont.

16. D flip-flop with asynchronous reset

17. 17
Master-slave D-type flip-flop
D Q
CLK
Input
Master D latch
D Q Output
Slave D latch
X
• How to make into negative edge-triggered D-
type flip-flop?

18. Analysis of Clocked Sequential Circuits
State diagrams:
• How do we characterize logic circuits?
– Combinational circuits: Truth tables
– Sequential circuits: State diagrams
• First draw the states
– States  Unique circuit configurations
• Second draw the transitions between states
– Transitions  Changes in state caused by inputs

19. Example1: A Sequential Circuit with D
Flip Flops

20. State Table for the Circuit (ex1)

21. State Diagram for the Circuit
(ex1)

22. Example2: A Sequential Circuit
with D Flip Flops

23. example3: A Sequential Circuit with JK
Flip Flops

24. State Table & Diagram for the
Circuit (ex3)

25. example4: A Sequential Circuit with T
Flip Flops

26. State Table for the Circuit (ex4)