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FA-91916 / PLC ladder logic scan cycles / Open access

CTU counts every scan the input is held · case 01

Holding the count input for several scans adds several counts instead of one.

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

ROOT CAUSE

The up-count condition tests the input level without its edge memory.

THE FAILURE

The up-count condition tests the input level without its edge memory.

Unsuccessful approach: Qualifying CU with the CD edge memory still miscounts when the two inputs differ.

Case contract

Up/down counter pair sharing one 16-bit signed accumulator, evaluated per scan; scans is a list of [cu, cd, res]. CU counts on its rising edge and CD on its own rising edge (both in one scan cancel). Incrementing 32767 wraps to -32768 and latches OV; decrementing -32768 wraps to 32767 and latches UN. A later RES rung clears ACC, OV and UN but not the edge memories. DN is ACC >= preset. Return [ACC, DN, OV, UN] 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, start, scans):
    acc = start
    ov = False
    un = False
    pcu = False
    pcd = False
    out = []
    for cu, cd, res in scans:
        cu = bool(cu)
        cd = bool(cd)
        if cu:
            acc += 1
            if acc > 32767:
                acc = -32768
                ov = True
        if cd and not pcd:
            acc -= 1
            if acc < -32768:
                acc = 32767
                un = True
        pcu = cu
        pcd = cd
        if res:
            acc = 0
            ov = False
            un = False
        out.append([acc, acc >= preset, ov, un])
    return out
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[['regression: held count input',
   [3, 0, [[True, False, False], [True, False, False], [False, False, False], [True, False, False]]],
   [[1, False, False, False], [1, False, False, False], [1, False, False, False], [2, False, False, False]]],
  ['regression: simultaneous edges',
   [1,
    0,
    [[True, True, False],
     [False, False, False],
     [True, False, False],
     [True, True, False],
     [False, True, False]]],
   [[0, False, False, False],
    [0, False, False, False],
    [1, True, False, False],
    [0, False, False, False],
    [0, False, False, False]]],
  ['control: overflow wrap',
   [0,
    32766,
    [[True, False, False],
     [False, False, False],
     [True, False, False],
     [False, False, False],
     [True, False, False]]],
   [[32767, True, False, False],
    [32767, True, False, False],
    [-32768, False, True, False],
    [-32768, False, True, False],
    [-32767, False, True, False]]],
  ['control: underflow then reset',
   [0,
    -32767,
    [[False, True, False],
     [False, False, False],
     [False, True, False],
     [False, False, True],
     [False, False, False]]],
   [[-32768, False, False, False],
    [-32768, False, False, False],
    [32767, True, False, True],
    [0, True, False, False],
    [0, True, False, False]]],
  ['regression: count down while up held',
   [0, 5, [[True, False, False], [True, True, False], [True, False, False], [True, True, False]]],
   [[6, True, False, False], [5, True, False, False], [5, True, False, False], [4, True, False, False]]],
  ['regression: scenario 1',
   [0,
    1,
    [[True, False, False],
     [True, False, False],
     [True, False, False],
     [False, True, True],
     [False, False, False],
     [True, False, False],
     [False, False, False],
     [False, False, False],
     [False, False, False]]],
   [[2, True, False, False],
    [2, True, False, False],
    [2, True, False, False],
    [0, True, False, False],
    [0, True, False, False],
    [1, True, False, False],
    [1, True, False, False],
    [1, True, False, False],
    [1, True, False, False]]],
  ['control: scenario 2',
   [3,
    32766,
    [[True, True, False],
     [False, False, False],
     [True, True, False],
     [False, False, True],
     [False, False, False],
     [True, False, False],
     [False, False, False],
     [True, True, False],
     [False, False, False],
     [True, True, False],
     [False, False, False],
     [False, True, False],
     [False, False, False]]],
   [[32766, True, False, False],
    [32766, True, False, False],
    [32766, True, False, False],
    [0, False, False, False],
    [0, False, False, False],
    [1, False, False, False],
    [1, False, False, False],
    [1, False, False, False],
    [1, False, False, False],
    [1, False, False, False],
    [1, False, False, False],
    [0, False, False, False],
    [0, False, False, False]]],
  ['regression: scenario 3',
   [0,
    32766,
    [[True, True, False],
     [True, True, False],
     [False, True, False],
     [True, True, False],
     [True, False, False],
     [False, True, True],
     [True, False, False],
     [True, False, False],
     [True, True, False],
     [False, False, False],
     [True, False, False]]],
   [[32766, True, False, False],
    [32766, True, False, False],
    [32766, True, False, False],
    [32767, True, False, False],
    [32767, True, False, False],
    [0, True, False, False],
    [1, True, False, False],
    [1, True, False, False],
    [0, True, False, False],
    [0, True, False, False],
    [1, True, False, False]]]],
 [['regression: simultaneous edges',
   [1,
    0,
    [[True, True, False],
     [False, False, False],
     [True, False, False],
     [True, True, False],
     [False, True, False]]],
   [[0, False, False, False],
    [0, False, False, False],
    [1, True, False, False],
    [0, False, False, False],
    [0, False, False, False]]],
  ['regression: count down while up held',
   [0, 5, [[True, False, False], [True, True, False], [True, False, False], [True, True, False]]],
   [[6, True, False, False], [5, True, False, False], [5, True, False, False], [4, True, False, False]]],
  ['regression: held count input',
   [3, 0, [[True, False, False], [True, False, False], [False, False, False], [True, False, False]]],
   [[1, False, False, False], [1, False, False, False], [1, False, False, False], [2, False, False, False]]],
  ['control: overflow wrap',
   [0,
    32766,
    [[True, False, False],
     [False, False, False],
     [True, False, False],
     [False, False, False],
     [True, False, False]]],
   [[32767, True, False, False],
    [32767, True, False, False],
    [-32768, False, True, False],
    [-32768, False, True, False],
    [-32767, False, True, False]]],
  ['control: underflow then reset',
   [0,
    -32767,
    [[False, True, False],
     [False, False, False],
     [False, True, False],
     [False, False, True],
     [False, False, False]]],
   [[-32768, False, False, False],
    [-32768, False, False, False],
    [32767, True, False, True],
    [0, True, False, False],
    [0, True, False, False]]],
  ['regression: scenario 1',
   [2,
    -32767,
    [[True, False, False],
     [True, False, False],
     [False, False, False],
     [False, False, False],
     [False, True, False],
     [False, False, False],
     [True, False, False],
     [True, False, False]]],
   [[-32766, False, False, False],
    [-32766, False, False, False],
    [-32766, False, False, False],
    [-32766, False, False, False],
    [-32767, False, False, False],
    [-32767, False, False, False],
    [-32766, False, False, False],
    [-32766, False, False, False]]],
  ['regression: scenario 2',
   [2,
    0,
    [[True, False, False],
     [False, False, False],
     [True, True, False],
     [False, False, False],
     [False, True, False],
     [False, False, False],
     [True, False, False],
     [True, True, False],
     [True, False, False],
     [False, False, False],
     [True, True, False]]],
   [[1, False, False, False],
    [1, False, False, False],
    [1, False, False, False],
    [1, False, False, False],
    [0, False, False, False],
    [0, False, False, False],
    [1, False, False, False],
    [0, False, False, False],
    [0, False, False, False],
    [0, False, False, False],
    [0, False, False, False]]],
  ['regression: scenario 3',
   [-1,
    32765,
    [[False, False, False],
     [False, False, True],
     [True, False, False],
     [False, False, False],
     [True, True, False],
     [True, False, False]]],
   [[32765, True, False, False],
    [0, True, False, False],
    [1, True, False, False],
    [1, True, False, False],
    [1, True, False, False],
    [1, True, False, False]]]],
 [['regression: count down while up held',
   [0, 5, [[True, False, False], [True, True, False], [True, False, False], [True, True, False]]],
   [[6, True, False, False], [5, True, False, False], [5, True, False, False], [4, True, False, False]]],
  ['regression: scenario 1',
   [3,
    32765,
    [[True, False, True],
     [True, False, False],
     [True, False, True],
     [False, True, False],
     [True, False, False],
     [True, True, True],
     [False, True, False],
     [False, False, False],
     [True, True, False],
     [False, True, False],
     [True, False, False],
     [False, False, False],
     [True, False, False],
     [False, True, False]]],
   [[0, False, False, False],
    [0, False, False, False],
    [0, False, False, False],
    [-1, False, False, False],
    [0, False, False, False],
    [0, False, False, False],
    [0, False, False, False],
    [0, False, False, False],
    [0, False, False, False],
    [0, False, False, False],
    [1, False, False, False],
    [1, False, False, False],
    [2, False, False, False],
    [1, False, False, False]]],
  ['regression: held count input',
   [3, 0, [[True, False, False], [True, False, False], [False, False, False], [True, False, False]]],
   [[1, False, False, False], [1, False, False, False], [1, False, False, False], [2, False, False, False]]],
  ['control: overflow wrap',
   [0,
    32766,
    [[True, False, False],
     [False, False, False],
     [True, False, False],
     [False, False, False],
     [True, False, False]]],
   [[32767, True, False, False],
    [32767, True, False, False],
    [-32768, False, True, False],
    [-32768, False, True, False],
    [-32767, False, True, False]]],
  ['control: underflow then reset',
   [0,
    -32767,
    [[False, True, False],
     [False, False, False],
     [False, True, False],
     [False, False, True],
     [False, False, False]]],
   [[-32768, False, False, False],
    [-32768, False, False, False],
    [32767, True, False, True],
    [0, True, False, False],
    [0, True, False, False]]],
  ['regression: simultaneous edges',
   [1,
    0,
    [[True, True, False],
     [False, False, False],
     [True, False, False],
     [True, True, False],
     [False, True, False]]],
   [[0, False, False, False],
    [0, False, False, False],
    [1, True, False, False],
    [0, False, False, False],
    [0, False, False, False]]],
  ['regression: scenario 2',
   [0,
    32765,
    [[False, False, False],
     [False, True, True],
     [True, False, False],
     [True, True, False],
     [False, False, False],
     [False, True, False],
     [True, False, False],
     [True, False, True],
     [True, False, False],
     [True, False, False],
     [True, False, False],
     [True, True, False],
     [True, False, False]]],
   [[32765, True, False, False],
    [0, True, False, False],
    [1, True, False, False],
    [0, True, False, False],
    [0, True, False, False],
    [-1, False, False, False],
    [0, True, False, False],
    [0, True, False, False],
    [0, True, False, False],
    [0, True, False, False],
    [0, True, False, False],
    [-1, False, False, False],
    [-1, False, False, False]]],
  ['regression: scenario 3',
   [0,
    32767,
    [[False, False, False],
     [False, False, False],
     [True, True, False],
     [True, False, True],
     [False, False, False],
     [False, False, False],
     [False, True, False],
     [False, False, False],
     [False, True, False],
     [True, False, False],
     [True, False, False],
     [False, True, False],
     [False, False, False],
     [False, False, False]]],
   [[32767, True, False, False],
    [32767, True, False, False],
    [32767, True, True, True],
    [0, True, False, False],
    [0, True, False, False],
    [0, True, False, False],
    [-1, False, False, False],
    [-1, False, False, False],
    [-2, False, False, False],
    [-1, False, False, False],
    [-1, False, False, False],
    [-2, False, False, False],
    [-2, False, False, False],
    [-2, False, False, False]]]],
 [['regression: scenario 1',
   [32767,
    32766,
    [[False, False, False],
     [True, True, False],
     [False, True, True],
     [True, True, False],
     [False, True, False],
     [True, False, False],
     [True, False, False],
     [True, False, False],
     [False, True, True],
     [True, False, False],
     [False, False, False],
     [False, False, False]]],
   [[32766, False, False, False],
    [32766, False, False, False],
    [0, False, False, False],
    [1, False, False, False],
    [1, False, False, False],
    [2, False, False, False],
    [2, False, False, False],
    [2, False, False, False],
    [0, False, False, False],
    [1, False, False, False],
    [1, False, False, False],
    [1, False, False, False]]],
  ['regression: scenario 2',
   [32767,
    -2,
    [[False, False, False],
     [True, False, False],
     [True, False, False],
     [True, False, False],
     [True, True, False],
     [False, False, False],
     [False, False, False],
     [False, True, False],
     [True, True, False]]],
   [[-2, False, False, False],
    [-1, False, False, False],
    [-1, False, False, False],
    [-1, False, False, False],
    [-2, False, False, False],
    [-2, False, False, False],
    [-2, False, False, False],
    [-3, False, False, False],
    [-2, False, False, False]]],
  ['regression: held count input',
   [3, 0, [[True, False, False], [True, False, False], [False, False, False], [True, False, False]]],
   [[1, False, False, False], [1, False, False, False], [1, False, False, False], [2, False, False, False]]],
  ['control: overflow wrap',
   [0,
    32766,
    [[True, False, False],
     [False, False, False],
     [True, False, False],
     [False, False, False],
     [True, False, False]]],
   [[32767, True, False, False],
    [32767, True, False, False],
    [-32768, False, True, False],
    [-32768, False, True, False],
    [-32767, False, True, False]]],
  ['control: underflow then reset',
   [0,
    -32767,
    [[False, True, False],
     [False, False, False],
     [False, True, False],
     [False, False, True],
     [False, False, False]]],
   [[-32768, False, False, False],
    [-32768, False, False, False],
    [32767, True, False, True],
    [0, True, False, False],
    [0, True, False, False]]],
  ['regression: simultaneous edges',
   [1,
    0,
    [[True, True, False],
     [False, False, False],
     [True, False, False],
     [True, True, False],
     [False, True, False]]],
   [[0, False, False, False],
    [0, False, False, False],
    [1, True, False, False],
    [0, False, False, False],
    [0, False, False, False]]],
  ['regression: count down while up held',
   [0, 5, [[True, False, False], [True, True, False], [True, False, False], [True, True, False]]],
   [[6, True, False, False], [5, True, False, False], [5, True, False, False], [4, True, False, False]]],
  ['regression: scenario 3',
   [5,
    32765,
    [[True, False, False],
     [True, False, False],
     [True, False, False],
     [True, True, False],
     [True, True, False],
     [True, False, False]]],
   [[32766, True, False, False],
    [32766, True, False, False],
    [32766, True, False, False],
    [32765, True, False, False],
    [32765, True, False, False],
    [32765, True, False, False]]]],
 [['regression: scenario 2',
   [32767,
    32765,
    [[False, True, False],
     [False, False, False],
     [True, False, False],
     [False, False, False],
     [True, False, False],
     [False, False, False],
     [True, False, True],
     [True, False, False],
     [False, True, False],
     [False, False, False],
     [True, False, False],
     [True, True, False]]],
   [[32764, False, False, False],
    [32764, False, False, False],
    [32765, False, False, False],
    [32765, False, False, False],
    [32766, False, False, False],
    [32766, False, False, False],
    [0, False, False, False],
    [0, False, False, False],
    [-1, False, False, False],
    [-1, False, False, False],
    [0, False, False, False],
    [-1, False, False, False]]],
  ['regression: scenario 3',
   [-32768,
    32767,
    [[False, False, False],
     [True, False, False],
     [False, True, False],
     [True, False, False],
     [False, True, False],
     [True, True, False],
     [True, False, False],
     [False, False, False],
     [False, False, False],
     [False, True, False],
     [True, False, True],
     [False, False, False],
     [True, False, False],
     [True, False, False]]],
   [[32767, True, False, False],
    [-32768, True, True, False],
    [32767, True, True, True],
    [-32768, True, True, True],
    [32767, True, True, True],
    [-32768, True, True, True],
    [-32768, True, True, True],
    [-32768, True, True, True],
    [-32768, True, True, True],
    [32767, True, True, True],
    [0, True, False, False],
    [0, True, False, False],
    [1, True, False, False],
    [1, True, False, False]]],
  ['regression: held count input',
   [3, 0, [[True, False, False], [True, False, False], [False, False, False], [True, False, False]]],
   [[1, False, False, False], [1, False, False, False], [1, False, False, False], [2, False, False, False]]],
  ['control: overflow wrap',
   [0,
    32766,
    [[True, False, False],
     [False, False, False],
     [True, False, False],
     [False, False, False],
     [True, False, False]]],
   [[32767, True, False, False],
    [32767, True, False, False],
    [-32768, False, True, False],
    [-32768, False, True, False],
    [-32767, False, True, False]]],
  ['control: underflow then reset',
   [0,
    -32767,
    [[False, True, False],
     [False, False, False],
     [False, True, False],
     [False, False, True],
     [False, False, False]]],
   [[-32768, False, False, False],
    [-32768, False, False, False],
    [32767, True, False, True],
    [0, True, False, False],
    [0, True, False, False]]],
  ['regression: simultaneous edges',
   [1,
    0,
    [[True, True, False],
     [False, False, False],
     [True, False, False],
     [True, True, False],
     [False, True, False]]],
   [[0, False, False, False],
    [0, False, False, False],
    [1, True, False, False],
    [0, False, False, False],
    [0, False, False, False]]],
  ['regression: count down while up held',
   [0, 5, [[True, False, False], [True, True, False], [True, False, False], [True, True, False]]],
   [[6, True, False, False], [5, True, False, False], [5, True, False, False], [4, True, False, False]]],
  ['regression: scenario 1',
   [0,
    -2,
    [[True, False, False],
     [False, False, False],
     [True, False, False],
     [True, True, False],
     [True, False, False],
     [False, False, True],
     [True, False, False],
     [True, False, False],
     [True, False, False],
     [False, True, False],
     [False, False, False],
     [True, False, False]]],
   [[-1, False, False, False],
    [-1, False, False, False],
    [0, True, False, False],
    [-1, False, False, False],
    [-1, False, False, False],
    [0, True, False, False],
    [1, True, False, False],
    [1, True, False, False],
    [1, True, False, False],
    [0, True, False, False],
    [0, True, False, False],
    [1, True, False, False]]]]]
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: held count input[[1, False, False, False], [2, False, False, False], [2, False, False, False], [3, True, False, False]][[1, False, False, False], [1, False, False, False], [1, False, False, False], [2, False, False, False]]Failed
regression: simultaneous edges[[0, False, False, False], [0, False, False, False], [1, True, False, False], [1, True, False, False], [1, True, False, False]][[0, False, False, False], [0, False, False, False], [1, True, False, False], [0, False, False, False], [0, False, False, False]]Failed
control: overflow wrap[[32767, True, False, False], [32767, True, False, False], [-32768, False, True, False], [-32768, False, True, False], [-32767, False, True, False]][[32767, True, False, False], [32767, True, False, False], [-32768, False, True, False], [-32768, False, True, False], [-32767, False, True, False]]Passed
control: underflow then reset[[-32768, False, False, False], [-32768, False, False, False], [32767, True, False, True], [0, True, False, False], [0, True, False, False]][[-32768, False, False, False], [-32768, False, False, False], [32767, True, False, True], [0, True, False, False], [0, True, False, False]]Passed
regression: count down while up held[[6, True, False, False], [6, True, False, False], [7, True, False, False], [7, True, False, False]][[6, True, False, False], [5, True, False, False], [5, True, False, False], [4, True, False, False]]Failed
regression: scenario 1[[2, True, False, False], [3, True, False, False], [4, True, False, False], [0, True, False, False], [0, True, False, False], [1, True, False, False], [1, True, False, False], [1, True, False, False], [1, True, False, False]][[2, True, False, False], [2, True, False, False], [2, True, False, False], [0, True, False, False], [0, True, False, False], [1, True, False, False], [1, True, False, False], [1, True, False, False], [1, True, False, False]]Failed
control: scenario 2[[32766, True, False, False], [32766, True, False, False], [32766, True, False, False], [0, False, False, False], [0, False, False, False], [1, False, False, False], [1, False, False, False], [1, False, False, False], [1, False, False, False], [1, False, False, False], [1, False, False, False], [0, False, False, False], [0, False, False, False]][[32766, True, False, False], [32766, True, False, False], [32766, True, False, False], [0, False, False, False], [0, False, False, False], [1, False, False, False], [1, False, False, False], [1, False, False, False], [1, False, False, False], [1, False, False, False], [1, False, False, False], [0, False, False, False], [0, False, False, False]]Passed
regression: scenario 3[[32766, True, False, False], [32767, True, False, False], [32767, True, False, False], [-32768, False, True, False], [-32767, False, True, False], [0, True, False, False], [1, True, False, False], [2, True, False, False], [2, True, False, False], [2, True, False, False], [3, True, False, False]][[32766, True, False, False], [32766, True, False, False], [32766, True, False, False], [32767, True, False, False], [32767, True, False, False], [0, True, False, False], [1, True, False, False], [1, True, False, False], [0, True, False, False], [0, True, False, False], [1, True, False, False]]Failed

SHA-256 / a2c84590810a99340070d4477e68db6dc82a537d8cd472186548f7211d592ac7

2 / The unsuccessful fix

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

N = 1
observations = []
def solve(preset, start, scans):
    acc = start
    ov = False
    un = False
    pcu = False
    pcd = False
    out = []
    for cu, cd, res in scans:
        cu = bool(cu)
        cd = bool(cd)
        if cu and not pcd:
            acc += 1
            if acc > 32767:
                acc = -32768
                ov = True
        if cd and not pcd:
            acc -= 1
            if acc < -32768:
                acc = 32767
                un = True
        pcu = cu
        pcd = cd
        if res:
            acc = 0
            ov = False
            un = False
        out.append([acc, acc >= preset, ov, un])
    return out
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[['regression: held count input',
   [3, 0, [[True, False, False], [True, False, False], [False, False, False], [True, False, False]]],
   [[1, False, False, False], [1, False, False, False], [1, False, False, False], [2, False, False, False]]],
  ['regression: simultaneous edges',
   [1,
    0,
    [[True, True, False],
     [False, False, False],
     [True, False, False],
     [True, True, False],
     [False, True, False]]],
   [[0, False, False, False],
    [0, False, False, False],
    [1, True, False, False],
    [0, False, False, False],
    [0, False, False, False]]],
  ['control: overflow wrap',
   [0,
    32766,
    [[True, False, False],
     [False, False, False],
     [True, False, False],
     [False, False, False],
     [True, False, False]]],
   [[32767, True, False, False],
    [32767, True, False, False],
    [-32768, False, True, False],
    [-32768, False, True, False],
    [-32767, False, True, False]]],
  ['control: underflow then reset',
   [0,
    -32767,
    [[False, True, False],
     [False, False, False],
     [False, True, False],
     [False, False, True],
     [False, False, False]]],
   [[-32768, False, False, False],
    [-32768, False, False, False],
    [32767, True, False, True],
    [0, True, False, False],
    [0, True, False, False]]],
  ['regression: count down while up held',
   [0, 5, [[True, False, False], [True, True, False], [True, False, False], [True, True, False]]],
   [[6, True, False, False], [5, True, False, False], [5, True, False, False], [4, True, False, False]]],
  ['regression: scenario 1',
   [0,
    1,
    [[True, False, False],
     [True, False, False],
     [True, False, False],
     [False, True, True],
     [False, False, False],
     [True, False, False],
     [False, False, False],
     [False, False, False],
     [False, False, False]]],
   [[2, True, False, False],
    [2, True, False, False],
    [2, True, False, False],
    [0, True, False, False],
    [0, True, False, False],
    [1, True, False, False],
    [1, True, False, False],
    [1, True, False, False],
    [1, True, False, False]]],
  ['control: scenario 2',
   [3,
    32766,
    [[True, True, False],
     [False, False, False],
     [True, True, False],
     [False, False, True],
     [False, False, False],
     [True, False, False],
     [False, False, False],
     [True, True, False],
     [False, False, False],
     [True, True, False],
     [False, False, False],
     [False, True, False],
     [False, False, False]]],
   [[32766, True, False, False],
    [32766, True, False, False],
    [32766, True, False, False],
    [0, False, False, False],
    [0, False, False, False],
    [1, False, False, False],
    [1, False, False, False],
    [1, False, False, False],
    [1, False, False, False],
    [1, False, False, False],
    [1, False, False, False],
    [0, False, False, False],
    [0, False, False, False]]],
  ['regression: scenario 3',
   [0,
    32766,
    [[True, True, False],
     [True, True, False],
     [False, True, False],
     [True, True, False],
     [True, False, False],
     [False, True, True],
     [True, False, False],
     [True, False, False],
     [True, True, False],
     [False, False, False],
     [True, False, False]]],
   [[32766, True, False, False],
    [32766, True, False, False],
    [32766, True, False, False],
    [32767, True, False, False],
    [32767, True, False, False],
    [0, True, False, False],
    [1, True, False, False],
    [1, True, False, False],
    [0, True, False, False],
    [0, True, False, False],
    [1, True, False, False]]]],
 [['regression: simultaneous edges',
   [1,
    0,
    [[True, True, False],
     [False, False, False],
     [True, False, False],
     [True, True, False],
     [False, True, False]]],
   [[0, False, False, False],
    [0, False, False, False],
    [1, True, False, False],
    [0, False, False, False],
    [0, False, False, False]]],
  ['regression: count down while up held',
   [0, 5, [[True, False, False], [True, True, False], [True, False, False], [True, True, False]]],
   [[6, True, False, False], [5, True, False, False], [5, True, False, False], [4, True, False, False]]],
  ['regression: held count input',
   [3, 0, [[True, False, False], [True, False, False], [False, False, False], [True, False, False]]],
   [[1, False, False, False], [1, False, False, False], [1, False, False, False], [2, False, False, False]]],
  ['control: overflow wrap',
   [0,
    32766,
    [[True, False, False],
     [False, False, False],
     [True, False, False],
     [False, False, False],
     [True, False, False]]],
   [[32767, True, False, False],
    [32767, True, False, False],
    [-32768, False, True, False],
    [-32768, False, True, False],
    [-32767, False, True, False]]],
  ['control: underflow then reset',
   [0,
    -32767,
    [[False, True, False],
     [False, False, False],
     [False, True, False],
     [False, False, True],
     [False, False, False]]],
   [[-32768, False, False, False],
    [-32768, False, False, False],
    [32767, True, False, True],
    [0, True, False, False],
    [0, True, False, False]]],
  ['regression: scenario 1',
   [2,
    -32767,
    [[True, False, False],
     [True, False, False],
     [False, False, False],
     [False, False, False],
     [False, True, False],
     [False, False, False],
     [True, False, False],
     [True, False, False]]],
   [[-32766, False, False, False],
    [-32766, False, False, False],
    [-32766, False, False, False],
    [-32766, False, False, False],
    [-32767, False, False, False],
    [-32767, False, False, False],
    [-32766, False, False, False],
    [-32766, False, False, False]]],
  ['regression: scenario 2',
   [2,
    0,
    [[True, False, False],
     [False, False, False],
     [True, True, False],
     [False, False, False],
     [False, True, False],
     [False, False, False],
     [True, False, False],
     [True, True, False],
     [True, False, False],
     [False, False, False],
     [True, True, False]]],
   [[1, False, False, False],
    [1, False, False, False],
    [1, False, False, False],
    [1, False, False, False],
    [0, False, False, False],
    [0, False, False, False],
    [1, False, False, False],
    [0, False, False, False],
    [0, False, False, False],
    [0, False, False, False],
    [0, False, False, False]]],
  ['regression: scenario 3',
   [-1,
    32765,
    [[False, False, False],
     [False, False, True],
     [True, False, False],
     [False, False, False],
     [True, True, False],
     [True, False, False]]],
   [[32765, True, False, False],
    [0, True, False, False],
    [1, True, False, False],
    [1, True, False, False],
    [1, True, False, False],
    [1, True, False, False]]]],
 [['regression: count down while up held',
   [0, 5, [[True, False, False], [True, True, False], [True, False, False], [True, True, False]]],
   [[6, True, False, False], [5, True, False, False], [5, True, False, False], [4, True, False, False]]],
  ['regression: scenario 1',
   [3,
    32765,
    [[True, False, True],
     [True, False, False],
     [True, False, True],
     [False, True, False],
     [True, False, False],
     [True, True, True],
     [False, True, False],
     [False, False, False],
     [True, True, False],
     [False, True, False],
     [True, False, False],
     [False, False, False],
     [True, False, False],
     [False, True, False]]],
   [[0, False, False, False],
    [0, False, False, False],
    [0, False, False, False],
    [-1, False, False, False],
    [0, False, False, False],
    [0, False, False, False],
    [0, False, False, False],
    [0, False, False, False],
    [0, False, False, False],
    [0, False, False, False],
    [1, False, False, False],
    [1, False, False, False],
    [2, False, False, False],
    [1, False, False, False]]],
  ['regression: held count input',
   [3, 0, [[True, False, False], [True, False, False], [False, False, False], [True, False, False]]],
   [[1, False, False, False], [1, False, False, False], [1, False, False, False], [2, False, False, False]]],
  ['control: overflow wrap',
   [0,
    32766,
    [[True, False, False],
     [False, False, False],
     [True, False, False],
     [False, False, False],
     [True, False, False]]],
   [[32767, True, False, False],
    [32767, True, False, False],
    [-32768, False, True, False],
    [-32768, False, True, False],
    [-32767, False, True, False]]],
  ['control: underflow then reset',
   [0,
    -32767,
    [[False, True, False],
     [False, False, False],
     [False, True, False],
     [False, False, True],
     [False, False, False]]],
   [[-32768, False, False, False],
    [-32768, False, False, False],
    [32767, True, False, True],
    [0, True, False, False],
    [0, True, False, False]]],
  ['regression: simultaneous edges',
   [1,
    0,
    [[True, True, False],
     [False, False, False],
     [True, False, False],
     [True, True, False],
     [False, True, False]]],
   [[0, False, False, False],
    [0, False, False, False],
    [1, True, False, False],
    [0, False, False, False],
    [0, False, False, False]]],
  ['regression: scenario 2',
   [0,
    32765,
    [[False, False, False],
     [False, True, True],
     [True, False, False],
     [True, True, False],
     [False, False, False],
     [False, True, False],
     [True, False, False],
     [True, False, True],
     [True, False, False],
     [True, False, False],
     [True, False, False],
     [True, True, False],
     [True, False, False]]],
   [[32765, True, False, False],
    [0, True, False, False],
    [1, True, False, False],
    [0, True, False, False],
    [0, True, False, False],
    [-1, False, False, False],
    [0, True, False, False],
    [0, True, False, False],
    [0, True, False, False],
    [0, True, False, False],
    [0, True, False, False],
    [-1, False, False, False],
    [-1, False, False, False]]],
  ['regression: scenario 3',
   [0,
    32767,
    [[False, False, False],
     [False, False, False],
     [True, True, False],
     [True, False, True],
     [False, False, False],
     [False, False, False],
     [False, True, False],
     [False, False, False],
     [False, True, False],
     [True, False, False],
     [True, False, False],
     [False, True, False],
     [False, False, False],
     [False, False, False]]],
   [[32767, True, False, False],
    [32767, True, False, False],
    [32767, True, True, True],
    [0, True, False, False],
    [0, True, False, False],
    [0, True, False, False],
    [-1, False, False, False],
    [-1, False, False, False],
    [-2, False, False, False],
    [-1, False, False, False],
    [-1, False, False, False],
    [-2, False, False, False],
    [-2, False, False, False],
    [-2, False, False, False]]]],
 [['regression: scenario 1',
   [32767,
    32766,
    [[False, False, False],
     [True, True, False],
     [False, True, True],
     [True, True, False],
     [False, True, False],
     [True, False, False],
     [True, False, False],
     [True, False, False],
     [False, True, True],
     [True, False, False],
     [False, False, False],
     [False, False, False]]],
   [[32766, False, False, False],
    [32766, False, False, False],
    [0, False, False, False],
    [1, False, False, False],
    [1, False, False, False],
    [2, False, False, False],
    [2, False, False, False],
    [2, False, False, False],
    [0, False, False, False],
    [1, False, False, False],
    [1, False, False, False],
    [1, False, False, False]]],
  ['regression: scenario 2',
   [32767,
    -2,
    [[False, False, False],
     [True, False, False],
     [True, False, False],
     [True, False, False],
     [True, True, False],
     [False, False, False],
     [False, False, False],
     [False, True, False],
     [True, True, False]]],
   [[-2, False, False, False],
    [-1, False, False, False],
    [-1, False, False, False],
    [-1, False, False, False],
    [-2, False, False, False],
    [-2, False, False, False],
    [-2, False, False, False],
    [-3, False, False, False],
    [-2, False, False, False]]],
  ['regression: held count input',
   [3, 0, [[True, False, False], [True, False, False], [False, False, False], [True, False, False]]],
   [[1, False, False, False], [1, False, False, False], [1, False, False, False], [2, False, False, False]]],
  ['control: overflow wrap',
   [0,
    32766,
    [[True, False, False],
     [False, False, False],
     [True, False, False],
     [False, False, False],
     [True, False, False]]],
   [[32767, True, False, False],
    [32767, True, False, False],
    [-32768, False, True, False],
    [-32768, False, True, False],
    [-32767, False, True, False]]],
  ['control: underflow then reset',
   [0,
    -32767,
    [[False, True, False],
     [False, False, False],
     [False, True, False],
     [False, False, True],
     [False, False, False]]],
   [[-32768, False, False, False],
    [-32768, False, False, False],
    [32767, True, False, True],
    [0, True, False, False],
    [0, True, False, False]]],
  ['regression: simultaneous edges',
   [1,
    0,
    [[True, True, False],
     [False, False, False],
     [True, False, False],
     [True, True, False],
     [False, True, False]]],
   [[0, False, False, False],
    [0, False, False, False],
    [1, True, False, False],
    [0, False, False, False],
    [0, False, False, False]]],
  ['regression: count down while up held',
   [0, 5, [[True, False, False], [True, True, False], [True, False, False], [True, True, False]]],
   [[6, True, False, False], [5, True, False, False], [5, True, False, False], [4, True, False, False]]],
  ['regression: scenario 3',
   [5,
    32765,
    [[True, False, False],
     [True, False, False],
     [True, False, False],
     [True, True, False],
     [True, True, False],
     [True, False, False]]],
   [[32766, True, False, False],
    [32766, True, False, False],
    [32766, True, False, False],
    [32765, True, False, False],
    [32765, True, False, False],
    [32765, True, False, False]]]],
 [['regression: scenario 2',
   [32767,
    32765,
    [[False, True, False],
     [False, False, False],
     [True, False, False],
     [False, False, False],
     [True, False, False],
     [False, False, False],
     [True, False, True],
     [True, False, False],
     [False, True, False],
     [False, False, False],
     [True, False, False],
     [True, True, False]]],
   [[32764, False, False, False],
    [32764, False, False, False],
    [32765, False, False, False],
    [32765, False, False, False],
    [32766, False, False, False],
    [32766, False, False, False],
    [0, False, False, False],
    [0, False, False, False],
    [-1, False, False, False],
    [-1, False, False, False],
    [0, False, False, False],
    [-1, False, False, False]]],
  ['regression: scenario 3',
   [-32768,
    32767,
    [[False, False, False],
     [True, False, False],
     [False, True, False],
     [True, False, False],
     [False, True, False],
     [True, True, False],
     [True, False, False],
     [False, False, False],
     [False, False, False],
     [False, True, False],
     [True, False, True],
     [False, False, False],
     [True, False, False],
     [True, False, False]]],
   [[32767, True, False, False],
    [-32768, True, True, False],
    [32767, True, True, True],
    [-32768, True, True, True],
    [32767, True, True, True],
    [-32768, True, True, True],
    [-32768, True, True, True],
    [-32768, True, True, True],
    [-32768, True, True, True],
    [32767, True, True, True],
    [0, True, False, False],
    [0, True, False, False],
    [1, True, False, False],
    [1, True, False, False]]],
  ['regression: held count input',
   [3, 0, [[True, False, False], [True, False, False], [False, False, False], [True, False, False]]],
   [[1, False, False, False], [1, False, False, False], [1, False, False, False], [2, False, False, False]]],
  ['control: overflow wrap',
   [0,
    32766,
    [[True, False, False],
     [False, False, False],
     [True, False, False],
     [False, False, False],
     [True, False, False]]],
   [[32767, True, False, False],
    [32767, True, False, False],
    [-32768, False, True, False],
    [-32768, False, True, False],
    [-32767, False, True, False]]],
  ['control: underflow then reset',
   [0,
    -32767,
    [[False, True, False],
     [False, False, False],
     [False, True, False],
     [False, False, True],
     [False, False, False]]],
   [[-32768, False, False, False],
    [-32768, False, False, False],
    [32767, True, False, True],
    [0, True, False, False],
    [0, True, False, False]]],
  ['regression: simultaneous edges',
   [1,
    0,
    [[True, True, False],
     [False, False, False],
     [True, False, False],
     [True, True, False],
     [False, True, False]]],
   [[0, False, False, False],
    [0, False, False, False],
    [1, True, False, False],
    [0, False, False, False],
    [0, False, False, False]]],
  ['regression: count down while up held',
   [0, 5, [[True, False, False], [True, True, False], [True, False, False], [True, True, False]]],
   [[6, True, False, False], [5, True, False, False], [5, True, False, False], [4, True, False, False]]],
  ['regression: scenario 1',
   [0,
    -2,
    [[True, False, False],
     [False, False, False],
     [True, False, False],
     [True, True, False],
     [True, False, False],
     [False, False, True],
     [True, False, False],
     [True, False, False],
     [True, False, False],
     [False, True, False],
     [False, False, False],
     [True, False, False]]],
   [[-1, False, False, False],
    [-1, False, False, False],
    [0, True, False, False],
    [-1, False, False, False],
    [-1, False, False, False],
    [0, True, False, False],
    [1, True, False, False],
    [1, True, False, False],
    [1, True, False, False],
    [0, True, False, False],
    [0, True, False, False],
    [1, True, False, False]]]]]
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: held count input[[1, False, False, False], [2, False, False, False], [2, False, False, False], [3, True, False, False]][[1, False, False, False], [1, False, False, False], [1, False, False, False], [2, False, False, False]]Failed
regression: simultaneous edges[[0, False, False, False], [0, False, False, False], [1, True, False, False], [1, True, False, False], [1, True, False, False]][[0, False, False, False], [0, False, False, False], [1, True, False, False], [0, False, False, False], [0, False, False, False]]Failed
control: overflow wrap[[32767, True, False, False], [32767, True, False, False], [-32768, False, True, False], [-32768, False, True, False], [-32767, False, True, False]][[32767, True, False, False], [32767, True, False, False], [-32768, False, True, False], [-32768, False, True, False], [-32767, False, True, False]]Passed
control: underflow then reset[[-32768, False, False, False], [-32768, False, False, False], [32767, True, False, True], [0, True, False, False], [0, True, False, False]][[-32768, False, False, False], [-32768, False, False, False], [32767, True, False, True], [0, True, False, False], [0, True, False, False]]Passed
regression: count down while up held[[6, True, False, False], [6, True, False, False], [6, True, False, False], [6, True, False, False]][[6, True, False, False], [5, True, False, False], [5, True, False, False], [4, True, False, False]]Failed
regression: scenario 1[[2, True, False, False], [3, True, False, False], [4, True, False, False], [0, True, False, False], [0, True, False, False], [1, True, False, False], [1, True, False, False], [1, True, False, False], [1, True, False, False]][[2, True, False, False], [2, True, False, False], [2, True, False, False], [0, True, False, False], [0, True, False, False], [1, True, False, False], [1, True, False, False], [1, True, False, False], [1, True, False, False]]Failed
control: scenario 2[[32766, True, False, False], [32766, True, False, False], [32766, True, False, False], [0, False, False, False], [0, False, False, False], [1, False, False, False], [1, False, False, False], [1, False, False, False], [1, False, False, False], [1, False, False, False], [1, False, False, False], [0, False, False, False], [0, False, False, False]][[32766, True, False, False], [32766, True, False, False], [32766, True, False, False], [0, False, False, False], [0, False, False, False], [1, False, False, False], [1, False, False, False], [1, False, False, False], [1, False, False, False], [1, False, False, False], [1, False, False, False], [0, False, False, False], [0, False, False, False]]Passed
regression: scenario 3[[32766, True, False, False], [32766, True, False, False], [32766, True, False, False], [32766, True, False, False], [32766, True, False, False], [0, True, False, False], [0, True, False, False], [1, True, False, False], [1, True, False, False], [1, True, False, False], [2, True, False, False]][[32766, True, False, False], [32766, True, False, False], [32766, True, False, False], [32767, True, False, False], [32767, True, False, False], [0, True, False, False], [1, True, False, False], [1, True, False, False], [0, True, False, False], [0, True, False, False], [1, True, False, False]]Failed

SHA-256 / b7fd2413257bac9665e63e5bcf8c6ec862faa37fddc59340a51c48465a8816d7

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 2026-09-29T14:51:40.717820+00:00.

Case digest / e8d446786cf96b75c34ce0d2c9afaa7db43a2b783ae0e8fa28341304e79c7329