The system LED

Every box has one LED, and it is the whole local diagnostic. What it can tell you depends on the line: some firmwares distinguish four states, others only two, because a box with no watchdog and no fatal handler cannot signal a crash.

What each line can show

Product line	LED states
CAN-CAN	4 states
CAN-MDV	4 states
CAN-ENOCEAN	2 states	no watchdog and no fatal handler, so a crash cannot be signalled
BLOC 8 v2	4 states
CAN-SERIAL	4 states

The codes

The LED	What it means
Blinking about once a second	running normally
Dark, with the box powered	not running — no firmware, or a fault before the application started
Steady on	stopped after startup
Blinking very fast, about 25 times a second	the firmware cannot confirm itself; power-cycle and it returns to the previous version

The last two are only produced on lines that report four states. On a two-state line, a box that has crashed looks the same as a box with no firmware: the LED simply does not blink. Read the bus rather than the LED — a box that answers readconfig is running.

TIP

A blinking LED means the application is alive; it says nothing about whether the box is addressed, whether the equipment behind it is answering, or whether anything is being published. A correctly running box that has never been given an instance blinks exactly like a working one.