FA-92187 / PLC ladder logic scan cycles / Member archive

FIFO empty bit is derived from the unloaded value · case 02

EM reports empty after a zero-valued part is unloaded even though entries remain, or not empty when drained of nonzero parts.

Member previewVariant 2 · 3 implementations · 8 checks per implementation

Case scope

EM reports empty after a zero-valued part is unloaded even though entries remain, or not empty when drained of nonzero parts.

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: single slot	`[[1, 0, true, true, [4]], [1, 0, true, true, [4]], [0, 4, false, false, [0]], [1, 4, true, false, [8]]]`	`[[1, 0, true, false, [4]], [1, 0, true, false, [4]], [0, 4, false, true, [0]], [1, 4, true, false, [8]]]`	Failed

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This record includes three runnable implementations, regression fixtures, execution results, and source hashes.

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