Base Direction is a term used to describe the direction the loco will go when told to go forward and is also one of the decoder's features that allow you to set and/or change the Base Direction.

With traditional DC Analog control, there is no base direction because there is no way to tell the loco to go forward. Physical direction is controlled by the polarity on the rails. Whether the loco goes forward or reverse depends on which way the loco is sitting on those rails. If you give it throttle and the loco goes the wrong direction, you simply flip the direction switch to make it go the other way, since there is no base direction control.

With DCC, the loco will go forward when you set it to go forward and it will go backwards when you tell it to go backwards - regardless of which way it's facing on the track, regardless of track polarity, and even going through a reverse section where the polarity changes beneath the loco.

The loco's Base Direction can be set and easily changed in several ways. This allows you to run various locos (such as the SD-9 for example) either long hood or short hood forward. It also allows for running two locos together, tail-to-tail or nose-to nose. But mostly, it allows DCC to make the train go forward when you tell it to go forward - regardless of where it is on the layout and which way it's facing on the track.

The Base Direction feature is just one of several ways to control a loco's direction. Other ways include CV19 (Decoder-Assisted Consisting), wiring the motor backwards, and direction control on the hand-held throttle. We'll discuss all this below.

1) Most decoders provide Base-Direction Programming. This is bit zero in CV 29 (more about this later). Decoders with this feature come with bit zero cleared - for forward direction. By setting bit zero, the base direction of travel will reverse - that is, when told to go forward it will go backward. There are reasons one might want to use this:

First, Base Direction is handy if your system doesn't support MU consisting and you want one loco in the consist to go backwards (for tail-to-tail consisting) when the lead loco is told to go forward. Refer to Decoder-Assisted Consisting for more information about MU Consisting.

Second, some locos were designed to run long hood forward, such as the SD-9, but some railroads ran them short hood forward. If you get a loco that is pre-wired for DCC to run long hood forward, but you want to run it short hood forward, all you have to do is set the Base Direction bit.

Some people errantly think this can be used to correct a wiring mistake (they connected the orange and gray wires to the motor backwards). But if the front and rear lights are wired correctly, setting the direction bit will also reverse them to make them wrong. If you make a mistake in decoder wiring, it's best to correct that mistake.

2) Many decoders have Decoder-Assisted Consisting. This uses CV19. When an address is programmed into CV19, bit 7 of that CV dictates loco direction. When bit 7 is clear, the base direction of the loco is unchanged. If set, the base direction of the loco is reversed from the direction bit 0 of CV 29 has it set for.

3) When wiring a decoder, the orange and gray wires are connected to the motor. The orange wire should connect to the "+" motor terminal - the one that was connected directly to the right rail (except for G scale) power pickup lead. The gray wire should connect to the "-" motor terminal - the one that was connected directly to the left rail (except for G scale) power pickup lead. G scale is backwards from all others: left rail is positive and right rail is negative. Wiring this way will produce a loco that will go forward when told to go forward and backward when told to go backward.

4) You have ultimate direction control of the train with your hand-held throttle. If everything is set up correctly, the train will go forward when you tell it to go forward with your throttle. But if for some reason it doesn't, all you have to do is press the direction button (or flip the direction switch, whichever your throttle has) and the loco will go the other direction.

Base Direction control is handled in the decoder. Once set in the decoder, it works on any system.

All decoders sold by Loy's Toys have this Base Direction control feature.

Base Direction is controlled by bit zero (0) of CV29. This means you need a system or other method for programming CV29.

All of Digitrax's systems have the capability to program Base Direction in CV29, and I'm fairly certain that all other currently available systems do also.

CV29 is a general overall loco configuration setting. Decoders come from the factory with CV29 programmed for loco forward when told to go forward (providing the motor is wired correctly). This feature is not intrusive. You do not need to bother with this unless you want to change the loco's base direction or need to recalculate the overall base loco configuration in CV29. Refer to CV Bit Manipulation for more information.