Edge 01 — Stuck start button
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Briefing
A START button can jam, or an operator can hold it down. A plain latched start/stop then restarts the motor the instant STOP is released, because START is still TRUE. Make the motor react to the press, not the hold: START counts once, when it goes from released to pressed. STOP always wins. To run again, START must be released and pressed anew.
Objectives
- A START press runs the motor, and it keeps running after release
- A STOP press stops it
- With START still held down, a STOP press stops the motor and it stays stopped
- Release START and press it again: the motor runs
Hints
- Hold START down and press STOP. What does your program do when STOP is released again while START is still down?
- The motor should respond to START changing from released to pressed, not to START being pressed. Which instruction produces a signal for exactly one scan when an input turns on?
- That one-scan signal is what should start the motor, while STOP keeps clearing it. A held START then only counts once.
- To prove it works, the motor must come back only after START is released and pressed again.
I/O Table
Inputs
START_PBStart push-button (momentary NO)
BOOL · %I0.0
STOP_PBStop push-button (TRUE = pressed)
BOOL · %I0.1
Outputs
MOTORMotor contactor
BOOL · %Q0.0
Your program will be tested against:
All test cases run automatically when you submit. Assertions are hidden until you pass.
- #1START pulse → MOTOR on
A momentary START runs the motor, and it keeps running after release
- #2STOP pulse → MOTOR off
STOP clears the run state
- #3START held down, STOP pressed and released → MOTOR stays off
A stuck START button must not restart the motor when STOP is released
- #4Release START and press it again → MOTOR runs
Each fresh press is a new start
Related scenarios
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