1. Analysis of Clocked Sequential Circuits

2. Example of a Sequential Circuit
D flip-flops

3. Example: Start with A=0, B=0, x=0.
A(next)=0
B(next)=0
Y(next)=0

4. What are A(next), B(next) and y(next) given that A=1, B=1 and X=1?
D flip-flops

5. Alternate State Table

6. State Diagram
Each circle is a state
When x=1, y=0.

7. State Diagram
Each circle is a state
When x=0, y=1.

8. Detects 0 in the bit stream of data
Output is a 0 as long as input is a 1. The first 0 after a string of 1 transfers the circuit back to 00.

9. Summary

10. Model a Clocked Sequential Circuit with Verilog
Use parameter to define constants
Form the next state from x and the
current state
Form the output
fork.....join construction S0 S2 S1 S3

11. Parameter S0 S2 S1 S3
Define states with parameter

12. Update States S0 S2 S1 S3 If reset is 0, set state to S0.
If reset is 1, update state with next_state. S1 S3

13. Implement the States Using State Diagram

14. fork....join

15. Right click to add state and next_state to the waveform shown right

16. Valid Mealy Output S0 S2 S1 S3

17. Mealy Glitches Glitiches occur because x changes before
the next rising clock edge S0 S2 S1 S3

18. General Structure of a Mealy Machine
Output depends on input as well as the state
The circuit is in. (variable: state)
Synchronize the input with clock when using Mealy machine.

19. Moore Machine
Output depends on the state, but not the input.

20. Synthesis of Sequential Circuit
Start with a state diagram
Assign Binary Values to the States

21. State Diagram for Sequence Detector
Problem statement:
Design a circuit that detects a sequence of three or more consecutive 1’s in a string of bits coming through an input line

22. State Diagram of the Word Description
Start with S0.
if input is 0, stay in S0.
if input is 1, go to S1.
Once in S1
if input is 1, go to S2.
if input is 0, go to S0.
Once in S2
if input is 1, go to S3.
Once in S3,
if input is 1, stay in S3, set output to 1.
Output is 1 when the circuit is in S3, 0 otherwise.

23. Assign Binary Value to the States1 2 3 4 5 6 7
Use two flip-flops to represent states.
Let x be the input
And y be the output

24. Assign Binary Value to the States1 2 3 4 5 6 7

25. Circuit Implementation

26. Sequence Detector Circuit
Random Number
generator

27. Measurement Results B A x y
clk