Lesson 4 — OR Stop
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Briefing
Two stop buttons — press either one and the light goes off. Both NC contacts must be closed (neither pressed) for the lamp to energise. This is the dual-stop safety pattern used in industrial panels everywhere.
Objectives
- LAMP is ON when neither STOP_1 nor STOP_2 is pressed
- LAMP goes OFF when STOP_1 is pressed
- LAMP goes OFF when STOP_2 is pressed
Hints
- Use two NC contacts (/ prefix) in series: if either STOP is pressed, power flow breaks.
- IEC: | /STOP_1 /STOP_2 | := LAMP ;
I/O Table
Inputs
STOP_1Stop button 1 (NC wired — closes on press)
BOOL · %I0.0
STOP_2Stop button 2 (NC wired — closes on press)
BOOL · %I0.1
Outputs
LAMPIndicator lamp
BOOL · %Q0.0
Your program will be tested against:
All test cases run automatically when you submit. Assertions are hidden until you pass.
- #1Neither stop pressed → LAMP on
Both NC contacts closed, power flows to lamp
- #2STOP_1 pressed → LAMP off
One stop breaks the series chain
- #3STOP_2 pressed → LAMP off
Other stop also breaks the chain
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