Go online to inspect the state of a Modicon application and investigate a reported fault. Use the diagnostic viewer for diagnostic messages, and consult the %S/%SW system information alongside an animation table to watch relevant variables. The example shows how those views change when a simulated pump or I/O connection changes state.
The diagnostic viewer is on the left and an animation table with four variables is on the right. Start the simulated pump, trip its overload or disconnect a RIO drop to see the messages and values change. The force control for Pump_Run demonstrates overriding a value. On real equipment, forcing can cause unexpected operation and must follow the approved test procedure with the required safeguards.
| Variable | Value | Modify |
|---|---|---|
| Pump_Run : EBOOL | FALSE | |
| Motor_Current | 3.1 | Not editable |
| Tank_Level | 42 | Not editable |
| RIO2_Health | OK | Not editable |
A forced value overrides normal control of that value. The force event in this log carries no system bit: %S19 is the task period overrun bit, not a force indicator. Check the actual CPU's system-bit reference. Record active forces and remove them before returning the equipment to service.
Start the investigation in this order: go online, read the diagnostic messages and watch the relevant variables in an animation table. The %SW system words provide controller status and timing information. Check their definitions against the CPU documentation before drawing conclusions from a value; a test override is a separate controlled action, not a repair.
📓 Diagnostic viewer shows the diagnostic information available from the configured application and controller. Use its messages and timestamps to narrow the investigation, then compare them with the live state and the CPU's diagnostic definitions.
👁️ Animation tables let you watch a selected set of variables as the program runs. Where supported, you can modify or force a value during an approved test. An override can defeat ordinary logic and cause movement; it is not inherently safe.
🚩 %S system bits include %S0 cold start, %S19 task period overrun, %S11 watchdog indication. Check the exact meanings and reset behaviour in the controller's system-bit reference.
📈 %SW system words contain numeric system information: %SW0 MAST period, %SW30–34 are shown here for timing information. Verify the individual word definitions for the CPU and task configuration in use.
A station entered STOP overnight and nobody saw the event. Which diagnostic information should you inspect first?