Category: PLC Basics
Elapsed Time Goes Negative After Clock Sync? Use the Right Clock
Wall-clock corrections can break duration calculations that subtract calendar timestamps.
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PLC Status Word Shows the Wrong Fault? Decode the Bit Map First
A status word may contain several independent flags rather than one fault number.
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PLC Reads 18 When the Device Shows 12? It Might Be BCD
A register that resembles an ordinary integer may contain binary-coded decimal.
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PLC Event Buffer Loses the Oldest Fault? Check Full Versus Empty
A circular buffer needs an explicit rule for becoming full.
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PLC Bit Shift Erases a Flag? Check Width and Direction
A shifted value depends on source width and the exact shift operation.
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PLC Converts a Barcode to Zero? Check the Parse Result
A failed numerical conversion must remain distinguishable from a valid zero.
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PLC Task Overlap Keeps Rising? A Faster Period Can Make It Worse
A periodic task needs enough time to finish before its next trigger.
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PLC Logic Looks Perfect but Never Runs? Trace the Call Path
A routine can exist in a project without executing.
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Two Devices Share One Timer State? Check the Function Block Instance
Two calls to one reusable definition do not automatically represent independent devices.
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PLC Timer Freezes When a Branch Is Skipped? False and Uncalled Differ
A timer receiving a false condition and a timer that is never executed are different situations.
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