Going online in Logix Designer turns your program into a live dashboard: rungs animate, tag values update in place, and a Trend charts any tag like a scope. Add a watch, force an input to test a theory, and read the controller fault log when something trips. Drive the machine below and watch all three react.
The Trend charts TankLevel live. Below, a watch list shows tags updating in place, and the fault log timestamps events. Start the pump and watch the level climb on the trend; force Pump_Cmd to override the logic (note the warning); trip an overload to log a major fault that faults the controller.
| Tag | Value | Force |
|---|---|---|
| Pump_Cmd | 0 | |
| TankLevel | 42.0 | n/a |
| Motor_Amps | 3.1 | n/a |
| Pump.Running | 0 | n/a |
Logix splits faults in two: a minor fault (like an arithmetic overflow) sets a bit and logs it but keeps running; a major fault (a watchdog, an array index out of range, a bad instruction) faults the controller to a stopped state unless you handle it in the fault routine. The fault log names the code and the rung, which is your fastest path to the cause. (The high-speed Trend can sample at the task rate to catch a glitch the eye misses.)
🔴 Online editing & animation: rungs colour live as they energise, and you can edit and accept changes on a running controller (with care). Values show right on the logic.
📈 Trends chart any tags over time, real-time or historical. This is the scope you reach for when a value "sometimes" misbehaves.
✊ Force I/O: pin an input or output to a value to test the wiring or the logic. The controller shows a prominent FORCES ENABLED warning while any force is active.
⚠ Controller log & faults: timestamped major/minor faults with codes, plus the controller log of mode changes and downloads. Treat it as the controller's black box.
Your code indexes an array one element past its end. If unhandled, what does Logix do?