Example: Traffic light controller
Highway intersected by farmroad
Detectors C sense cars on farmroad
- No car on farmroad: Hwy light remains green
- Car on farmroad: Hwy lights grn ? ylw ? red; farmroad lights ? grn
- Farmroad lights stay green only as long as a farmroad car is detected
- Never longer than a prescribed interval
- End farmroad: Farm lights grn ? ylw ? red; hwy lights ? grn
- Hwy stays green for at least a prescribed interval
Interval timer generates
- Short time pulse (TS) and a long time pulse (TL)
- ...in response to a set (ST) signal
- TS times yellow lights
- TL times green lights