S5f1

S5F1/S5F2 is the SECS-II message pair equipment uses to report an alarm condition to the host — spontaneous, equipment-initiated notification carrying an Alarm Identifier (ALID), an alarm code indicating set or clear, and descriptive alarm text, following the same unsolicited pattern as S6F11's collection-event reporting rather than a host-requested query. S5F1 (Alarm Report Send) is sent the moment equipment detects an alarm condition transitioning — either newly set or newly cleared — and S5F2 (Alarm Report Send Acknowledge) is the host's simple confirmation of receipt; unlike collection events, which require the define/link/enable setup chain before they flow, alarm reporting in GEM is typically always active rather than needing to be separately configured per alarm.

The set/clear distinction carried in S5F1 is what lets a host track an alarm's full lifecycle rather than just knowing it happened once — equipment reports the alarm both when the condition first becomes true (set) and again when it resolves (clear), which means a host that only reacts to the "set" report and ignores "clear" reports will keep treating a long-resolved alarm as still active, exactly the kind of state-tracking bug that produces false alarm backlogs and operator alert fatigue over time. Because alarm reporting bypasses the collection-event define/link/enable chain, it is also one of the few GEM mechanisms that a host can generally rely on working immediately on any compliant tool without prior configuration, which is a deliberate design choice — safety-relevant notifications should not depend on a host having correctly completed an optional setup sequence first.

S5F1/S5F2 is deliberately independent of the collection-event setup chain (S2F33 through S2F38) that governs ordinary process data reporting, since alarm notification is treated as a baseline safety mechanism rather than an optional, host-configured feature — this is also why alarm identifiers are typically documented in a tool's Common Equipment Model (SEMI E120) alongside status variables and equipment constants, so a host integration knows what every ALID it might receive actually means.