FA-92284 / PLC ladder logic scan cycles / Member archive

Two-hand window start is not cleared when both hands release · case 04

After a failed attempt, a new correct two-hand press is refused because the window is measured from the old press.

Member previewVariant 4 · 3 implementations · 8 checks per implementation

Case contract

Two-hand press control sampled per scan; samples is a list of [t_ms, left, right]. The press may start only when both buttons become pressed within window ms of the first one being pressed (inclusive), starting from a state where both were released. Releasing either button stops the press, and both buttons must then be released before a new start is allowed (anti-tie-down). Return the run output per scan.

Why this case matters

Ladder programs are executed as repeated scans; each defect here changes what a rung, timer, counter or data-table instruction reports on a particular scan, which is how commissioning and field faults are actually observed.

One recorded failure

Sample boundary fixture

This sample comes from the broken implementation of a controlled reproducer.

Boundary fixture	Actual	Expected	Outcome
regression: scenario 3	`[false, false, false, false, false, false, false, false, false, false, false, false, false, false]`	`[false, false, false, false, false, false, false, false, true, false, false, false, true, false]`	Failed

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