What is feedback on a DCC controller?

Most modellers will be aware of how a controller makes a locomotive move along the tracks, with an analogue controller, the more power that is sent from the controller, the quicker the train moves, reversing the polarity reverses the direction of travel. The actions of the controller (and therefore the train) are a direct result of the actions of the person operating it.

A DCC controller works differently, the person operating the controller can't send more or less power to the engine because a DCC model engine has full power supplied to it at all times through the constantly powered tracks. Instead, what the operator does is sends a message (carried as a code within the AC the current) to the engine's decoder, the decoder then regulates and distributes the power accordingly to control movement, lights and sound etc in compliance with the instruction received.

A DCC controller (as good as it is) can only send information one way though, this means that a controller can't recognise a particular train or its capabilities, all it can do is send commands to an address, and if there are two locomotives present on the layout with the same address, they will both react to that command, furthermore, if an engine's decoder isn't programmed correctly, the command may not be executed at all. This system is far from limiting though and is not usually an issue for most home layouts with most modellers becoming quite accustomed to programming their decoders effectively, resulting in hours of entertainment being had with things just the way they are, however, for more advanced layouts, there is a system where the controller and decoder can have two-way communication.

It is this ability for a decoder to communicate back with a controller that is known as feedback, it is employed on systems such as Railcom, and it allows controllers to instantly recognise the presence of an engine on a layout, it will know all about that particular engine including what functions are available and more importantly where the engine is on the layout, this information makes it possible to track all of your engine's locations and movements on a screen back at the control panel and also makes it possible to control your engines without having to endlessly program addresses and function numbers into a keypad.

This kind of setup is great for modellers' with large complicated layouts and for operating them with a degree of operational realism, but the really exciting prospect is what model developers and manufacturers will do with this technology next!