Which option correctly describes OSR in PLCs?

• A. A signal that remains high for every scan
• B. The rising edge of a signal detected once per cycle
• C. An output module with rapid switching
• D. One Shot Rising, stays true for one PLC scan

Answer: (D)

OSR is a One-Shot Rising instruction: it generates a pulse that lasts for exactly one PLC scan when the input makes a rising transition from false to true. If the input stays high, the output does not stay high beyond that one scan, and it will fire again only on a subsequent rising edge after the input goes low. This makes it ideal for triggering a single action per rising edge, such as starting a process or advancing a step, regardless of how long the input remains asserted. The chosen description captures this behavior by stating it stays true for one PLC scan. The other options either describe a signal that remains high continuously, or a generic edge detect that doesn’t imply the one-scan pulse behavior, or refer to hardware rather than the logic function.