Auto Reverse is an electronic feature found in some boosters. If the phase on the rails between two power districts controlled by different boosters do not match, a short will occur. To prevent that, both rails are gapped to isolate one power district from the other. When a metal wheel bridges the gap, if the phase is mismatched a short occurs. The auto reverse circuit detects that event, and flips the phase so they match.
Auto reversing devices are available, to implement automated phase matching on a Reverse Loop. They can be part of a Power Management device, or a stand-alone unit from suppliers such as Digitrax.
If a train enters a Reverse Loop or ballon track, at the turnout Rail A will connect to Rail B through the turnout (or switch). To prevent this, there must be double gaps on the track loop.
The auto reverser will detect when there is a phase mismatch across a gap, such as that found in a reverse loop or turntable, and instantly correct the situation. Any situation where Rail A connects to Rail B will result in a short circuit. The DCC signal rapidly switches from one rail to the other, while the other rail is held to ground until it switches rails again. This is why connecting Rail A to B results in a short. This also causes a short when two booster districts are out of phase.
DCCWiki.Com Is a great source of DCC Topics to help the beginner all the way to the expert. Also don't forget to check the manufactures website as well.