@Vernon Barry posted:The logic behind the above statements and why it matters:
While DCS is a signal on the track, it is bi-directional meaning the TIU talks to the loco, and the loco talks back to the TIU.
An engine must have track power- to be able to respond and reply back to a DCS command back to the TIU.
An unpowered engine (engine sitting on track that is not powered at the moment) cannot reply- to a read request- hence is "not on the track" hence is deemed "inactive".
An engine powered on the track, but not started, sitting idle, no lights, no sounds- still is possible to respond to DCS commands because it does have track power.
These are concepts that I have read about, however haven't remembered. The last one does take me aback a little, as I am used to seeing some "life" a light or sound when a track is powered. Obviously old old school... 
