When a Modicon misbehaves, you go online and look. Two windows do the work: the diagnostic viewer (a timestamped log of every event and the %S/%SW system bits) and the animation table — your live watch-and-force window onto any variable. Poke the machine below and watch both react.
Left is the diagnostic viewer; right is an animation table monitoring four variables. Every action on the deck — start the pump, trip an overload, drop a RIO drop — lands in the viewer with a timestamp and a system bit. Force Pump_Run from the table and watch it override the logic (with a warning), exactly as on a real ePAC.
| Variable | Value | Modify |
|---|---|---|
| Pump_Run : EBOOL | FALSE | |
| Motor_Current | 3.1 | — |
| Tank_Level | 42 | — |
| RIO2_Health | OK | — |
A forced value is held by you, overriding the logic and the wire. The ePAC flags %S19 while any force is active — clear them before you leave.
The Modicon debug ritual: go online → read the diagnostic viewer → watch the suspect variables in an animation table → force an input to test a theory. The %SW system words even tell you the scan time and which task overran — the ePAC narrates its own health if you know where to look.
📓 Diagnostic viewer — the timestamped event log: mode changes, module faults, application errors, with the system bit that flagged each. First place to look, always.
👁️ Animation tables — build a list of any variables and watch them update live; modify or force a handful to test wiring and logic safely.
🚩 %S system bits — %S0 cold start, %S19 scan overrun/force active, %S11 watchdog… one-bit health flags your logic can read too.
📈 %SW system words — diagnostics as numbers: %SW0 MAST period, %SW30–34 scan times, fault counters. The data behind the events.
A station tripped to STOP overnight and nobody saw it. What's the single fastest way to find out why?