When a machine misbehaves at 2am, three tools find the fault for you: online monitoring, the event log, and the EtherCAT bus diagnostics that point straight at the failed node. This lesson starts by hunting down a dropped slave.
EtherCAT is a daisy-chain: the frame visits each slave in order. When one drops, everything after it goes dark too, so the first "unreachable" node, or the cable into it, is your culprit. Press the fault, then click the node you think failed.
Controller event log
🔍 Online + breakpoints. Watch live variable values as the program runs; set a breakpoint to freeze on a condition and step line by line. Force a value to test a branch without rewiring.
📈 Data Trace samples variables every task cycle into a scope view. That is how you see a glitch that's gone before your eye can catch it.
📋 Event log + error codes. The controller timestamps every fault with a code you can look up. Read it first, because it usually names the unit and the cause.
🧭 The method: reproduce → read the log → narrow with trace/breakpoints → fix → confirm. Don't guess; let the controller tell you.
On an EtherCAT chain, slaves 3, 4 and 5 all report unreachable at once. Where's the most likely fault?