Factorio Forums

I have noticed something i don't quite understand. When i read the contents of a train via the circuit network, it sometimes seems to not output an item that was loaded on the train just as it leaves a station. I would expect that an item can only loaded on to a train if the train is stopped and that i can read the added contents via the circuit network (even if only for 1 tick).

Am i missing something or what is going on here?

The item is added to the train inventory the moment the inserter swing is completed and the item has disappeared from the inserter hand. Not when the inserter is starting to swing while holding the item.
Similar to combinator processing, there is also some latency involved between signal changes and output of that signal change.
It seems the waiting conditions are processed the same tick as items are added to the train, so if you have the "inventory full" condition, the train disconnects from the station and is about to leave the same tick the circuit info would be output, and since it's just disconnected, the info from that last tick isn't appearing externally.
As far as I remember, I once wanted to do something if the train is full, but it wasn't possible to send the train some final signal - it already left the tick before.