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

State table of Mealy Machine x X1 X2 S S1 S2 S3 S Y S1 Y2 S2 Y1 S3 Y3

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

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

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.

Timing Diagram Specification

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

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

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

Asynchronous sr flip-flop

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

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

Negated sr FF

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