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FA-91871 / PLC ladder logic scan cycles / Open access

TOF output energizes at power-up with a false rung · case 01

After a restart the off-delay output is on for a full preset even though its rung was never true.

Verified by executionVariant 1 · 8 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

The timer is initialized as freshly de-energized (ACC 0, DN set) instead of expired.

THE FAILURE

The timer is initialized as freshly de-energized (ACC 0, DN set) instead of expired.

Unsuccessful approach: Zeroing only the accumulator keeps DN off but reports a wrong power-up ACC value.

Case contract

Off-delay timer (TOF) evaluated once per scan; scans is a list of [rung_in, elapsed_ms]. At power-up the timer is expired (ACC = preset, DN false). A true rung clears ACC and sets DN. After the rung drops, ACC accumulates each later false scan's elapsed time (the true-to-false scan itself is not credited), clamped at preset, and DN clears when ACC >= preset. TT is DN and not rung_in. Return [DN, TT, ACC] 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.

1 / The failure

Exit 1
"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(preset, scans):
    acc = 0
    dn = True
    prev = False
    out = []
    for rung_in, dt in scans:
        rung_in = bool(rung_in)
        if rung_in:
            acc = 0
            dn = True
        elif dn:
            if not prev:
                acc = min(preset, acc + dt)
            if acc >= preset:
                dn = False
        tt = dn and not rung_in
        prev = rung_in
        out.append([dn, tt, acc])
    return out
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[['regression: power-up with false rung',
   [60, [[False, 20], [False, 20], [False, 20], [True, 10]]],
   [[False, False, 60], [False, False, 60], [False, False, 60], [True, False, 0]]],
  ['regression: scenario 1',
   [60, [[False, 70], [True, 10], [True, 70], [True, 10], [False, 70], [False, 10], [True, 10], [False, 30]]],
   [[False, False, 60],
    [True, False, 0],
    [True, False, 0],
    [True, False, 0],
    [True, True, 0],
    [True, True, 10],
    [True, False, 0],
    [True, True, 0]]],
  ['control: re-energized mid delay',
   [100, [[True, 10], [False, 40], [False, 40], [True, 40], [False, 40], [False, 40], [False, 40]]],
   [[True, False, 0],
    [True, True, 0],
    [True, True, 40],
    [True, False, 0],
    [True, True, 0],
    [True, True, 40],
    [True, True, 80]]],
  ['control: zero preset drop',
   [0, [[True, 10], [False, 10], [False, 10]]],
   [[True, False, 0], [False, False, 0], [False, False, 0]]],
  ['control: exact expiry',
   [60, [[True, 10], [False, 30], [False, 30], [False, 30], [False, 30]]],
   [[True, False, 0], [True, True, 0], [True, True, 30], [False, False, 60], [False, False, 60]]],
  ['regression: scenario 2',
   [60, [[False, 30], [True, 50], [True, 20], [True, 30], [True, 70], [False, 50], [False, 50], [False, 70]]],
   [[False, False, 60],
    [True, False, 0],
    [True, False, 0],
    [True, False, 0],
    [True, False, 0],
    [True, True, 0],
    [True, True, 50],
    [False, False, 60]]],
  ['control: scenario 3',
   [40,
    [[True, 70],
     [True, 0],
     [False, 50],
     [True, 30],
     [False, 0],
     [False, 50],
     [False, 30],
     [False, 50],
     [False, 10],
     [True, 20]]],
   [[True, False, 0],
    [True, False, 0],
    [True, True, 0],
    [True, False, 0],
    [True, True, 0],
    [False, False, 40],
    [False, False, 40],
    [False, False, 40],
    [False, False, 40],
    [True, False, 0]]],
  ['regression: scenario 4',
   [100,
    [[False, 30],
     [False, 70],
     [True, 30],
     [False, 30],
     [False, 20],
     [False, 50],
     [False, 70],
     [True, 50],
     [True, 50],
     [False, 20],
     [False, 50]]],
   [[False, False, 100],
    [False, False, 100],
    [True, False, 0],
    [True, True, 0],
    [True, True, 20],
    [True, True, 70],
    [False, False, 100],
    [True, False, 0],
    [True, False, 0],
    [True, True, 0],
    [True, True, 50]]]],
 [['regression: scenario 3',
   [150,
    [[False, 50],
     [False, 10],
     [False, 0],
     [False, 50],
     [True, 50],
     [False, 70],
     [False, 10],
     [True, 70],
     [False, 50],
     [False, 70],
     [False, 20],
     [True, 50],
     [False, 0],
     [True, 30]]],
   [[False, False, 150],
    [False, False, 150],
    [False, False, 150],
    [False, False, 150],
    [True, False, 0],
    [True, True, 0],
    [True, True, 10],
    [True, False, 0],
    [True, True, 0],
    [True, True, 70],
    [True, True, 90],
    [True, False, 0],
    [True, True, 0],
    [True, False, 0]]],
  ['regression: scenario 4',
   [60,
    [[False, 0],
     [False, 10],
     [True, 20],
     [False, 20],
     [False, 0],
     [False, 0],
     [True, 50],
     [True, 20],
     [True, 10],
     [True, 0],
     [True, 10],
     [False, 20],
     [False, 70]]],
   [[False, False, 60],
    [False, False, 60],
    [True, False, 0],
    [True, True, 0],
    [True, True, 0],
    [True, True, 0],
    [True, False, 0],
    [True, False, 0],
    [True, False, 0],
    [True, False, 0],
    [True, False, 0],
    [True, True, 0],
    [False, False, 60]]],
  ['regression: power-up with false rung',
   [60, [[False, 20], [False, 20], [False, 20], [True, 10]]],
   [[False, False, 60], [False, False, 60], [False, False, 60], [True, False, 0]]],
  ['control: re-energized mid delay',
   [100, [[True, 10], [False, 40], [False, 40], [True, 40], [False, 40], [False, 40], [False, 40]]],
   [[True, False, 0],
    [True, True, 0],
    [True, True, 40],
    [True, False, 0],
    [True, True, 0],
    [True, True, 40],
    [True, True, 80]]],
  ['control: zero preset drop',
   [0, [[True, 10], [False, 10], [False, 10]]],
   [[True, False, 0], [False, False, 0], [False, False, 0]]],
  ['control: exact expiry',
   [60, [[True, 10], [False, 30], [False, 30], [False, 30], [False, 30]]],
   [[True, False, 0], [True, True, 0], [True, True, 30], [False, False, 60], [False, False, 60]]],
  ['control: scenario 1',
   [0, [[False, 30], [True, 20], [True, 30], [False, 50], [True, 0], [True, 50], [True, 50]]],
   [[False, False, 0],
    [True, False, 0],
    [True, False, 0],
    [False, False, 0],
    [True, False, 0],
    [True, False, 0],
    [True, False, 0]]],
  ['control: scenario 2',
   [0, [[False, 10], [True, 0], [True, 70], [False, 0], [True, 70], [False, 20], [False, 10]]],
   [[False, False, 0],
    [True, False, 0],
    [True, False, 0],
    [False, False, 0],
    [True, False, 0],
    [False, False, 0],
    [False, False, 0]]]],
 [['regression: scenario 7',
   [60, [[False, 30], [True, 0], [True, 20], [True, 30], [False, 0], [False, 0], [True, 30]]],
   [[False, False, 60],
    [True, False, 0],
    [True, False, 0],
    [True, False, 0],
    [True, True, 0],
    [True, True, 0],
    [True, False, 0]]],
  ['regression: scenario 10',
   [60, [[False, 20], [False, 10], [True, 70], [False, 0], [False, 70], [True, 10], [False, 0], [True, 0]]],
   [[False, False, 60],
    [False, False, 60],
    [True, False, 0],
    [True, True, 0],
    [False, False, 60],
    [True, False, 0],
    [True, True, 0],
    [True, False, 0]]],
  ['regression: power-up with false rung',
   [60, [[False, 20], [False, 20], [False, 20], [True, 10]]],
   [[False, False, 60], [False, False, 60], [False, False, 60], [True, False, 0]]],
  ['control: re-energized mid delay',
   [100, [[True, 10], [False, 40], [False, 40], [True, 40], [False, 40], [False, 40], [False, 40]]],
   [[True, False, 0],
    [True, True, 0],
    [True, True, 40],
    [True, False, 0],
    [True, True, 0],
    [True, True, 40],
    [True, True, 80]]],
  ['control: zero preset drop',
   [0, [[True, 10], [False, 10], [False, 10]]],
   [[True, False, 0], [False, False, 0], [False, False, 0]]],
  ['control: exact expiry',
   [60, [[True, 10], [False, 30], [False, 30], [False, 30], [False, 30]]],
   [[True, False, 0], [True, True, 0], [True, True, 30], [False, False, 60], [False, False, 60]]],
  ['control: scenario 1',
   [0,
    [[False, 50],
     [True, 10],
     [False, 0],
     [True, 20],
     [False, 70],
     [False, 50],
     [True, 70],
     [False, 10],
     [False, 10],
     [False, 20],
     [True, 70]]],
   [[False, False, 0],
    [True, False, 0],
    [False, False, 0],
    [True, False, 0],
    [False, False, 0],
    [False, False, 0],
    [True, False, 0],
    [False, False, 0],
    [False, False, 0],
    [False, False, 0],
    [True, False, 0]]],
  ['control: scenario 2',
   [0,
    [[False, 30],
     [True, 50],
     [False, 50],
     [True, 0],
     [True, 10],
     [True, 10],
     [False, 10],
     [False, 50],
     [False, 10]]],
   [[False, False, 0],
    [True, False, 0],
    [False, False, 0],
    [True, False, 0],
    [True, False, 0],
    [True, False, 0],
    [False, False, 0],
    [False, False, 0],
    [False, False, 0]]]],
 [['regression: scenario 11',
   [100, [[False, 20], [True, 70], [False, 30], [False, 20], [False, 10], [False, 30], [True, 30]]],
   [[False, False, 100],
    [True, False, 0],
    [True, True, 0],
    [True, True, 20],
    [True, True, 30],
    [True, True, 60],
    [True, False, 0]]],
  ['regression: scenario 6',
   [40,
    [[False, 70],
     [True, 30],
     [True, 0],
     [False, 20],
     [True, 30],
     [False, 50],
     [True, 70],
     [True, 0],
     [False, 50]]],
   [[False, False, 40],
    [True, False, 0],
    [True, False, 0],
    [True, True, 0],
    [True, False, 0],
    [True, True, 0],
    [True, False, 0],
    [True, False, 0],
    [True, True, 0]]],
  ['regression: power-up with false rung',
   [60, [[False, 20], [False, 20], [False, 20], [True, 10]]],
   [[False, False, 60], [False, False, 60], [False, False, 60], [True, False, 0]]],
  ['control: re-energized mid delay',
   [100, [[True, 10], [False, 40], [False, 40], [True, 40], [False, 40], [False, 40], [False, 40]]],
   [[True, False, 0],
    [True, True, 0],
    [True, True, 40],
    [True, False, 0],
    [True, True, 0],
    [True, True, 40],
    [True, True, 80]]],
  ['control: zero preset drop',
   [0, [[True, 10], [False, 10], [False, 10]]],
   [[True, False, 0], [False, False, 0], [False, False, 0]]],
  ['control: exact expiry',
   [60, [[True, 10], [False, 30], [False, 30], [False, 30], [False, 30]]],
   [[True, False, 0], [True, True, 0], [True, True, 30], [False, False, 60], [False, False, 60]]],
  ['control: scenario 1',
   [40, [[True, 70], [True, 20], [True, 20], [False, 30], [False, 30], [False, 0], [False, 70], [False, 20]]],
   [[True, False, 0],
    [True, False, 0],
    [True, False, 0],
    [True, True, 0],
    [True, True, 30],
    [True, True, 30],
    [False, False, 40],
    [False, False, 40]]],
  ['regression: scenario 2',
   [100,
    [[False, 30],
     [False, 20],
     [True, 20],
     [True, 10],
     [True, 70],
     [False, 20],
     [False, 10],
     [True, 20],
     [False, 0],
     [True, 0],
     [True, 0]]],
   [[False, False, 100],
    [False, False, 100],
    [True, False, 0],
    [True, False, 0],
    [True, False, 0],
    [True, True, 0],
    [True, True, 10],
    [True, False, 0],
    [True, True, 0],
    [True, False, 0],
    [True, False, 0]]]],
 [['regression: scenario 10',
   [150,
    [[False, 30],
     [True, 70],
     [False, 20],
     [False, 30],
     [False, 20],
     [False, 10],
     [False, 20],
     [False, 30],
     [True, 70],
     [True, 10],
     [False, 70],
     [False, 20]]],
   [[False, False, 150],
    [True, False, 0],
    [True, True, 0],
    [True, True, 30],
    [True, True, 50],
    [True, True, 60],
    [True, True, 80],
    [True, True, 110],
    [True, False, 0],
    [True, False, 0],
    [True, True, 0],
    [True, True, 20]]],
  ['regression: scenario 8',
   [40,
    [[False, 0],
     [False, 20],
     [True, 70],
     [True, 30],
     [False, 20],
     [False, 20],
     [True, 50],
     [False, 0],
     [False, 20],
     [False, 0],
     [False, 50],
     [False, 30],
     [False, 50],
     [True, 0]]],
   [[False, False, 40],
    [False, False, 40],
    [True, False, 0],
    [True, False, 0],
    [True, True, 0],
    [True, True, 20],
    [True, False, 0],
    [True, True, 0],
    [True, True, 20],
    [True, True, 20],
    [False, False, 40],
    [False, False, 40],
    [False, False, 40],
    [True, False, 0]]],
  ['regression: power-up with false rung',
   [60, [[False, 20], [False, 20], [False, 20], [True, 10]]],
   [[False, False, 60], [False, False, 60], [False, False, 60], [True, False, 0]]],
  ['control: re-energized mid delay',
   [100, [[True, 10], [False, 40], [False, 40], [True, 40], [False, 40], [False, 40], [False, 40]]],
   [[True, False, 0],
    [True, True, 0],
    [True, True, 40],
    [True, False, 0],
    [True, True, 0],
    [True, True, 40],
    [True, True, 80]]],
  ['control: zero preset drop',
   [0, [[True, 10], [False, 10], [False, 10]]],
   [[True, False, 0], [False, False, 0], [False, False, 0]]],
  ['control: exact expiry',
   [60, [[True, 10], [False, 30], [False, 30], [False, 30], [False, 30]]],
   [[True, False, 0], [True, True, 0], [True, True, 30], [False, False, 60], [False, False, 60]]],
  ['control: scenario 1',
   [40,
    [[True, 70], [True, 20], [False, 50], [False, 20], [False, 50], [False, 50], [False, 50], [False, 0]]],
   [[True, False, 0],
    [True, False, 0],
    [True, True, 0],
    [True, True, 20],
    [False, False, 40],
    [False, False, 40],
    [False, False, 40],
    [False, False, 40]]],
  ['regression: scenario 2',
   [40,
    [[False, 70],
     [True, 70],
     [False, 50],
     [True, 70],
     [False, 10],
     [False, 30],
     [True, 0],
     [True, 50],
     [False, 0],
     [False, 30]]],
   [[False, False, 40],
    [True, False, 0],
    [True, True, 0],
    [True, False, 0],
    [True, True, 0],
    [True, True, 30],
    [True, False, 0],
    [True, False, 0],
    [True, True, 0],
    [True, True, 30]]]]]
for label, args, expected in fixtures[N-1]:
    check(label, solve(*args), expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)
Boundary fixtureActualExpectedOutcome
regression: power-up with false rung[[True, True, 20], [True, True, 40], [False, False, 60], [True, False, 0]][[False, False, 60], [False, False, 60], [False, False, 60], [True, False, 0]]Failed
regression: scenario 1[[False, False, 60], [True, False, 0], [True, False, 0], [True, False, 0], [True, True, 0], [True, True, 10], [True, False, 0], [True, True, 0]][[False, False, 60], [True, False, 0], [True, False, 0], [True, False, 0], [True, True, 0], [True, True, 10], [True, False, 0], [True, True, 0]]Passed
control: re-energized mid delay[[True, False, 0], [True, True, 0], [True, True, 40], [True, False, 0], [True, True, 0], [True, True, 40], [True, True, 80]][[True, False, 0], [True, True, 0], [True, True, 40], [True, False, 0], [True, True, 0], [True, True, 40], [True, True, 80]]Passed
control: zero preset drop[[True, False, 0], [False, False, 0], [False, False, 0]][[True, False, 0], [False, False, 0], [False, False, 0]]Passed
control: exact expiry[[True, False, 0], [True, True, 0], [True, True, 30], [False, False, 60], [False, False, 60]][[True, False, 0], [True, True, 0], [True, True, 30], [False, False, 60], [False, False, 60]]Passed
regression: scenario 2[[True, True, 30], [True, False, 0], [True, False, 0], [True, False, 0], [True, False, 0], [True, True, 0], [True, True, 50], [False, False, 60]][[False, False, 60], [True, False, 0], [True, False, 0], [True, False, 0], [True, False, 0], [True, True, 0], [True, True, 50], [False, False, 60]]Failed
control: scenario 3[[True, False, 0], [True, False, 0], [True, True, 0], [True, False, 0], [True, True, 0], [False, False, 40], [False, False, 40], [False, False, 40], [False, False, 40], [True, False, 0]][[True, False, 0], [True, False, 0], [True, True, 0], [True, False, 0], [True, True, 0], [False, False, 40], [False, False, 40], [False, False, 40], [False, False, 40], [True, False, 0]]Passed
regression: scenario 4[[True, True, 30], [False, False, 100], [True, False, 0], [True, True, 0], [True, True, 20], [True, True, 70], [False, False, 100], [True, False, 0], [True, False, 0], [True, True, 0], [True, True, 50]][[False, False, 100], [False, False, 100], [True, False, 0], [True, True, 0], [True, True, 20], [True, True, 70], [False, False, 100], [True, False, 0], [True, False, 0], [True, True, 0], [True, True, 50]]Failed

SHA-256 / acc6a3b3769770ab7f7ed4ef35d347b37501b6352cbdebccdfb56993fcb08e17

2 / The unsuccessful fix

Exit 1
"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(preset, scans):
    acc = 0
    dn = False
    prev = False
    out = []
    for rung_in, dt in scans:
        rung_in = bool(rung_in)
        if rung_in:
            acc = 0
            dn = True
        elif dn:
            if not prev:
                acc = min(preset, acc + dt)
            if acc >= preset:
                dn = False
        tt = dn and not rung_in
        prev = rung_in
        out.append([dn, tt, acc])
    return out
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[['regression: power-up with false rung',
   [60, [[False, 20], [False, 20], [False, 20], [True, 10]]],
   [[False, False, 60], [False, False, 60], [False, False, 60], [True, False, 0]]],
  ['regression: scenario 1',
   [60, [[False, 70], [True, 10], [True, 70], [True, 10], [False, 70], [False, 10], [True, 10], [False, 30]]],
   [[False, False, 60],
    [True, False, 0],
    [True, False, 0],
    [True, False, 0],
    [True, True, 0],
    [True, True, 10],
    [True, False, 0],
    [True, True, 0]]],
  ['control: re-energized mid delay',
   [100, [[True, 10], [False, 40], [False, 40], [True, 40], [False, 40], [False, 40], [False, 40]]],
   [[True, False, 0],
    [True, True, 0],
    [True, True, 40],
    [True, False, 0],
    [True, True, 0],
    [True, True, 40],
    [True, True, 80]]],
  ['control: zero preset drop',
   [0, [[True, 10], [False, 10], [False, 10]]],
   [[True, False, 0], [False, False, 0], [False, False, 0]]],
  ['control: exact expiry',
   [60, [[True, 10], [False, 30], [False, 30], [False, 30], [False, 30]]],
   [[True, False, 0], [True, True, 0], [True, True, 30], [False, False, 60], [False, False, 60]]],
  ['regression: scenario 2',
   [60, [[False, 30], [True, 50], [True, 20], [True, 30], [True, 70], [False, 50], [False, 50], [False, 70]]],
   [[False, False, 60],
    [True, False, 0],
    [True, False, 0],
    [True, False, 0],
    [True, False, 0],
    [True, True, 0],
    [True, True, 50],
    [False, False, 60]]],
  ['control: scenario 3',
   [40,
    [[True, 70],
     [True, 0],
     [False, 50],
     [True, 30],
     [False, 0],
     [False, 50],
     [False, 30],
     [False, 50],
     [False, 10],
     [True, 20]]],
   [[True, False, 0],
    [True, False, 0],
    [True, True, 0],
    [True, False, 0],
    [True, True, 0],
    [False, False, 40],
    [False, False, 40],
    [False, False, 40],
    [False, False, 40],
    [True, False, 0]]],
  ['regression: scenario 4',
   [100,
    [[False, 30],
     [False, 70],
     [True, 30],
     [False, 30],
     [False, 20],
     [False, 50],
     [False, 70],
     [True, 50],
     [True, 50],
     [False, 20],
     [False, 50]]],
   [[False, False, 100],
    [False, False, 100],
    [True, False, 0],
    [True, True, 0],
    [True, True, 20],
    [True, True, 70],
    [False, False, 100],
    [True, False, 0],
    [True, False, 0],
    [True, True, 0],
    [True, True, 50]]]],
 [['regression: scenario 3',
   [150,
    [[False, 50],
     [False, 10],
     [False, 0],
     [False, 50],
     [True, 50],
     [False, 70],
     [False, 10],
     [True, 70],
     [False, 50],
     [False, 70],
     [False, 20],
     [True, 50],
     [False, 0],
     [True, 30]]],
   [[False, False, 150],
    [False, False, 150],
    [False, False, 150],
    [False, False, 150],
    [True, False, 0],
    [True, True, 0],
    [True, True, 10],
    [True, False, 0],
    [True, True, 0],
    [True, True, 70],
    [True, True, 90],
    [True, False, 0],
    [True, True, 0],
    [True, False, 0]]],
  ['regression: scenario 4',
   [60,
    [[False, 0],
     [False, 10],
     [True, 20],
     [False, 20],
     [False, 0],
     [False, 0],
     [True, 50],
     [True, 20],
     [True, 10],
     [True, 0],
     [True, 10],
     [False, 20],
     [False, 70]]],
   [[False, False, 60],
    [False, False, 60],
    [True, False, 0],
    [True, True, 0],
    [True, True, 0],
    [True, True, 0],
    [True, False, 0],
    [True, False, 0],
    [True, False, 0],
    [True, False, 0],
    [True, False, 0],
    [True, True, 0],
    [False, False, 60]]],
  ['regression: power-up with false rung',
   [60, [[False, 20], [False, 20], [False, 20], [True, 10]]],
   [[False, False, 60], [False, False, 60], [False, False, 60], [True, False, 0]]],
  ['control: re-energized mid delay',
   [100, [[True, 10], [False, 40], [False, 40], [True, 40], [False, 40], [False, 40], [False, 40]]],
   [[True, False, 0],
    [True, True, 0],
    [True, True, 40],
    [True, False, 0],
    [True, True, 0],
    [True, True, 40],
    [True, True, 80]]],
  ['control: zero preset drop',
   [0, [[True, 10], [False, 10], [False, 10]]],
   [[True, False, 0], [False, False, 0], [False, False, 0]]],
  ['control: exact expiry',
   [60, [[True, 10], [False, 30], [False, 30], [False, 30], [False, 30]]],
   [[True, False, 0], [True, True, 0], [True, True, 30], [False, False, 60], [False, False, 60]]],
  ['control: scenario 1',
   [0, [[False, 30], [True, 20], [True, 30], [False, 50], [True, 0], [True, 50], [True, 50]]],
   [[False, False, 0],
    [True, False, 0],
    [True, False, 0],
    [False, False, 0],
    [True, False, 0],
    [True, False, 0],
    [True, False, 0]]],
  ['control: scenario 2',
   [0, [[False, 10], [True, 0], [True, 70], [False, 0], [True, 70], [False, 20], [False, 10]]],
   [[False, False, 0],
    [True, False, 0],
    [True, False, 0],
    [False, False, 0],
    [True, False, 0],
    [False, False, 0],
    [False, False, 0]]]],
 [['regression: scenario 7',
   [60, [[False, 30], [True, 0], [True, 20], [True, 30], [False, 0], [False, 0], [True, 30]]],
   [[False, False, 60],
    [True, False, 0],
    [True, False, 0],
    [True, False, 0],
    [True, True, 0],
    [True, True, 0],
    [True, False, 0]]],
  ['regression: scenario 10',
   [60, [[False, 20], [False, 10], [True, 70], [False, 0], [False, 70], [True, 10], [False, 0], [True, 0]]],
   [[False, False, 60],
    [False, False, 60],
    [True, False, 0],
    [True, True, 0],
    [False, False, 60],
    [True, False, 0],
    [True, True, 0],
    [True, False, 0]]],
  ['regression: power-up with false rung',
   [60, [[False, 20], [False, 20], [False, 20], [True, 10]]],
   [[False, False, 60], [False, False, 60], [False, False, 60], [True, False, 0]]],
  ['control: re-energized mid delay',
   [100, [[True, 10], [False, 40], [False, 40], [True, 40], [False, 40], [False, 40], [False, 40]]],
   [[True, False, 0],
    [True, True, 0],
    [True, True, 40],
    [True, False, 0],
    [True, True, 0],
    [True, True, 40],
    [True, True, 80]]],
  ['control: zero preset drop',
   [0, [[True, 10], [False, 10], [False, 10]]],
   [[True, False, 0], [False, False, 0], [False, False, 0]]],
  ['control: exact expiry',
   [60, [[True, 10], [False, 30], [False, 30], [False, 30], [False, 30]]],
   [[True, False, 0], [True, True, 0], [True, True, 30], [False, False, 60], [False, False, 60]]],
  ['control: scenario 1',
   [0,
    [[False, 50],
     [True, 10],
     [False, 0],
     [True, 20],
     [False, 70],
     [False, 50],
     [True, 70],
     [False, 10],
     [False, 10],
     [False, 20],
     [True, 70]]],
   [[False, False, 0],
    [True, False, 0],
    [False, False, 0],
    [True, False, 0],
    [False, False, 0],
    [False, False, 0],
    [True, False, 0],
    [False, False, 0],
    [False, False, 0],
    [False, False, 0],
    [True, False, 0]]],
  ['control: scenario 2',
   [0,
    [[False, 30],
     [True, 50],
     [False, 50],
     [True, 0],
     [True, 10],
     [True, 10],
     [False, 10],
     [False, 50],
     [False, 10]]],
   [[False, False, 0],
    [True, False, 0],
    [False, False, 0],
    [True, False, 0],
    [True, False, 0],
    [True, False, 0],
    [False, False, 0],
    [False, False, 0],
    [False, False, 0]]]],
 [['regression: scenario 11',
   [100, [[False, 20], [True, 70], [False, 30], [False, 20], [False, 10], [False, 30], [True, 30]]],
   [[False, False, 100],
    [True, False, 0],
    [True, True, 0],
    [True, True, 20],
    [True, True, 30],
    [True, True, 60],
    [True, False, 0]]],
  ['regression: scenario 6',
   [40,
    [[False, 70],
     [True, 30],
     [True, 0],
     [False, 20],
     [True, 30],
     [False, 50],
     [True, 70],
     [True, 0],
     [False, 50]]],
   [[False, False, 40],
    [True, False, 0],
    [True, False, 0],
    [True, True, 0],
    [True, False, 0],
    [True, True, 0],
    [True, False, 0],
    [True, False, 0],
    [True, True, 0]]],
  ['regression: power-up with false rung',
   [60, [[False, 20], [False, 20], [False, 20], [True, 10]]],
   [[False, False, 60], [False, False, 60], [False, False, 60], [True, False, 0]]],
  ['control: re-energized mid delay',
   [100, [[True, 10], [False, 40], [False, 40], [True, 40], [False, 40], [False, 40], [False, 40]]],
   [[True, False, 0],
    [True, True, 0],
    [True, True, 40],
    [True, False, 0],
    [True, True, 0],
    [True, True, 40],
    [True, True, 80]]],
  ['control: zero preset drop',
   [0, [[True, 10], [False, 10], [False, 10]]],
   [[True, False, 0], [False, False, 0], [False, False, 0]]],
  ['control: exact expiry',
   [60, [[True, 10], [False, 30], [False, 30], [False, 30], [False, 30]]],
   [[True, False, 0], [True, True, 0], [True, True, 30], [False, False, 60], [False, False, 60]]],
  ['control: scenario 1',
   [40, [[True, 70], [True, 20], [True, 20], [False, 30], [False, 30], [False, 0], [False, 70], [False, 20]]],
   [[True, False, 0],
    [True, False, 0],
    [True, False, 0],
    [True, True, 0],
    [True, True, 30],
    [True, True, 30],
    [False, False, 40],
    [False, False, 40]]],
  ['regression: scenario 2',
   [100,
    [[False, 30],
     [False, 20],
     [True, 20],
     [True, 10],
     [True, 70],
     [False, 20],
     [False, 10],
     [True, 20],
     [False, 0],
     [True, 0],
     [True, 0]]],
   [[False, False, 100],
    [False, False, 100],
    [True, False, 0],
    [True, False, 0],
    [True, False, 0],
    [True, True, 0],
    [True, True, 10],
    [True, False, 0],
    [True, True, 0],
    [True, False, 0],
    [True, False, 0]]]],
 [['regression: scenario 10',
   [150,
    [[False, 30],
     [True, 70],
     [False, 20],
     [False, 30],
     [False, 20],
     [False, 10],
     [False, 20],
     [False, 30],
     [True, 70],
     [True, 10],
     [False, 70],
     [False, 20]]],
   [[False, False, 150],
    [True, False, 0],
    [True, True, 0],
    [True, True, 30],
    [True, True, 50],
    [True, True, 60],
    [True, True, 80],
    [True, True, 110],
    [True, False, 0],
    [True, False, 0],
    [True, True, 0],
    [True, True, 20]]],
  ['regression: scenario 8',
   [40,
    [[False, 0],
     [False, 20],
     [True, 70],
     [True, 30],
     [False, 20],
     [False, 20],
     [True, 50],
     [False, 0],
     [False, 20],
     [False, 0],
     [False, 50],
     [False, 30],
     [False, 50],
     [True, 0]]],
   [[False, False, 40],
    [False, False, 40],
    [True, False, 0],
    [True, False, 0],
    [True, True, 0],
    [True, True, 20],
    [True, False, 0],
    [True, True, 0],
    [True, True, 20],
    [True, True, 20],
    [False, False, 40],
    [False, False, 40],
    [False, False, 40],
    [True, False, 0]]],
  ['regression: power-up with false rung',
   [60, [[False, 20], [False, 20], [False, 20], [True, 10]]],
   [[False, False, 60], [False, False, 60], [False, False, 60], [True, False, 0]]],
  ['control: re-energized mid delay',
   [100, [[True, 10], [False, 40], [False, 40], [True, 40], [False, 40], [False, 40], [False, 40]]],
   [[True, False, 0],
    [True, True, 0],
    [True, True, 40],
    [True, False, 0],
    [True, True, 0],
    [True, True, 40],
    [True, True, 80]]],
  ['control: zero preset drop',
   [0, [[True, 10], [False, 10], [False, 10]]],
   [[True, False, 0], [False, False, 0], [False, False, 0]]],
  ['control: exact expiry',
   [60, [[True, 10], [False, 30], [False, 30], [False, 30], [False, 30]]],
   [[True, False, 0], [True, True, 0], [True, True, 30], [False, False, 60], [False, False, 60]]],
  ['control: scenario 1',
   [40,
    [[True, 70], [True, 20], [False, 50], [False, 20], [False, 50], [False, 50], [False, 50], [False, 0]]],
   [[True, False, 0],
    [True, False, 0],
    [True, True, 0],
    [True, True, 20],
    [False, False, 40],
    [False, False, 40],
    [False, False, 40],
    [False, False, 40]]],
  ['regression: scenario 2',
   [40,
    [[False, 70],
     [True, 70],
     [False, 50],
     [True, 70],
     [False, 10],
     [False, 30],
     [True, 0],
     [True, 50],
     [False, 0],
     [False, 30]]],
   [[False, False, 40],
    [True, False, 0],
    [True, True, 0],
    [True, False, 0],
    [True, True, 0],
    [True, True, 30],
    [True, False, 0],
    [True, False, 0],
    [True, True, 0],
    [True, True, 30]]]]]
for label, args, expected in fixtures[N-1]:
    check(label, solve(*args), expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)
Boundary fixtureActualExpectedOutcome
regression: power-up with false rung[[False, False, 0], [False, False, 0], [False, False, 0], [True, False, 0]][[False, False, 60], [False, False, 60], [False, False, 60], [True, False, 0]]Failed
regression: scenario 1[[False, False, 0], [True, False, 0], [True, False, 0], [True, False, 0], [True, True, 0], [True, True, 10], [True, False, 0], [True, True, 0]][[False, False, 60], [True, False, 0], [True, False, 0], [True, False, 0], [True, True, 0], [True, True, 10], [True, False, 0], [True, True, 0]]Failed
control: re-energized mid delay[[True, False, 0], [True, True, 0], [True, True, 40], [True, False, 0], [True, True, 0], [True, True, 40], [True, True, 80]][[True, False, 0], [True, True, 0], [True, True, 40], [True, False, 0], [True, True, 0], [True, True, 40], [True, True, 80]]Passed
control: zero preset drop[[True, False, 0], [False, False, 0], [False, False, 0]][[True, False, 0], [False, False, 0], [False, False, 0]]Passed
control: exact expiry[[True, False, 0], [True, True, 0], [True, True, 30], [False, False, 60], [False, False, 60]][[True, False, 0], [True, True, 0], [True, True, 30], [False, False, 60], [False, False, 60]]Passed
regression: scenario 2[[False, False, 0], [True, False, 0], [True, False, 0], [True, False, 0], [True, False, 0], [True, True, 0], [True, True, 50], [False, False, 60]][[False, False, 60], [True, False, 0], [True, False, 0], [True, False, 0], [True, False, 0], [True, True, 0], [True, True, 50], [False, False, 60]]Failed
control: scenario 3[[True, False, 0], [True, False, 0], [True, True, 0], [True, False, 0], [True, True, 0], [False, False, 40], [False, False, 40], [False, False, 40], [False, False, 40], [True, False, 0]][[True, False, 0], [True, False, 0], [True, True, 0], [True, False, 0], [True, True, 0], [False, False, 40], [False, False, 40], [False, False, 40], [False, False, 40], [True, False, 0]]Passed
regression: scenario 4[[False, False, 0], [False, False, 0], [True, False, 0], [True, True, 0], [True, True, 20], [True, True, 70], [False, False, 100], [True, False, 0], [True, False, 0], [True, True, 0], [True, True, 50]][[False, False, 100], [False, False, 100], [True, False, 0], [True, True, 0], [True, True, 20], [True, True, 70], [False, False, 100], [True, False, 0], [True, False, 0], [True, True, 0], [True, True, 50]]Failed

SHA-256 / 78d4a29a43df711c1cb7b3bb98cb971303658f56314cff697143e85ed45d9c24

HELD IN THE MEMBER ARCHIVE

The verified repair and its recorded checks are member-only.

This mechanism has 8 recorded checks per implementation. The open-access tier publishes the failure and the unsuccessful fix; the repaired source that passes every check, and the observations that prove it, are available to members.

Every case sharing this mechanism uses the same contract and the same repair, so this one record is held back for all of them.

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Verification & scope

A deterministic bounded teaching model of one PLC instruction or rung pattern evaluated scan by scan. The stated contract is a stipulated toy convention, not a claim of conformance to any vendor controller or IEC 61131-3 runtime. This reproducer isolates one failure mechanism. Results cover the supplied fixtures. Variants within a family share a test contract and should remain grouped when constructing evaluation splits. Related mechanisms with a shared evaluation_group must also remain together; these controlled models are not independent production incidents.

Observations recorded using Python 3.12.14 at 2026-09-29T14:51:40.179624+00:00.

Case digest / d8e4603ca228533ae80dce106c7858028b176ed32bad01f7999c64856cbcc2b5