1. Mealy Machine x X1 X2 S S1 S2 S3 x X1 X2 S S1 Y1 Y2 S2 Y3 S3 outputs
state X X1 X2 S S1 S2 Y1 Y2 S3 Y3

2. State table of Mealy Machinex X1 X2 S S1 S2 S3 S Y S1 Y2 S2 Y1 S3 Y3

3. Mealy Machine Graph X2/Y2 X X1 X2 S S1 S2 Y1 Y2 S3 Y3 X2/Y1 X1/Y1 S1

4. Moore Machine Graph X2 x X1 X2 Y S S1 S2 Y2 S3 Y1 Y3 X1 S1/Y2 X2 S2/Y1

5. Natural language formulation of a problem
Design a control unit for ligth signalization on the railway with car sensors in positions A, B, C. The cars can go BA, AB i AC.
In direction BA go only car sets of length larger than the distance between sensors B and A.
In directions AB and AC go only single cars of length smaller than distance between sensors A and B and A and C, respectively.
The designed circuit should light lamp
z=1 if there are no cars between sensors A and B or sensors A and C
Sensors A, B, C generate signals a=1, b=1 and c=1 respectively, when sets of cars or single cars occur to be in their close distance.

6. Timing Diagram Specification

7. Transition and output table for light signalization circuit
ABC
000
001
011
010
110
111
101
100 Z S S1 - S6 S2 S3 1 S5 S4 S7 S8

8. Moore Machine graph for the analyzed device
010
6/1
110
1/0
100
000
000
7/1
2/1
000
100
8/1
001
5/1
3/1
000
010
4/1

9. asynchronous flip-flop sr
Q(t+1)
Q(t) 1 -
Q(t)Q(t+1) s r - 1

10. Asynchronous sr flip-flop

11. Asynchronous flip-flop sr
Q(t+1)
Q(t) 1 -

12. Negated sr FF This version has negated inputs
This FF realizes the function:
Q(t+1) - 1
Q(t)
Q(t)Q(t+1) - 1

13. Negated sr FF

14. Negated sr FF
Q(t+1) - 1
Q(t)