CV - Configuration Variables

Every DCC decoder can be programmed to respond to a specific direction. Loco decoders also can be programmed to use 14, 28 or 128 speed steps, acceleration delay, braking delay, etc. Accesory decoders can change the time of output activation. The features are stored in special locations of internal decoder memory. These locations are called Configuration Variables or simply CV.

CV programming is done from Command Station in diferent modes of programming (direct, register, paged, PoM) not all decoders accept all programming modes so you have to check it in the decoder manual.

The main accepted CV for most loco and function decoders are:

CV1Decoder address (1 - 99)
CV2Starting Voltage
CV3Acceleration delay
CV4Deceleration delay
CV5Maximum speed
CV7Decoder Version (only read)
CV8Manufacturer ID (only read)
CV17-CV18Extended address (1 - 9999). Have to be programmed in a special way:

CV19Multi unit (consist) address
CV29Decoder Configuration
This is calculated from its bits
Bit 0 -> 0: Direction normal, 1: Direction inverted
Bit 1 -> 0: 14 speed steps, 1: 28 / 128 speed steps
Bit 2 -> 0: Only DCC, 1: DCC and DC
Bit 3 -> 0: RailCom off, 1: RailCom on
Bit 4 -> 0: Factory preset speed curve, 1: User speed curve
Bit 5 -> 0: Address in CV1, 1: Address in CV17-CV18

CV29 7 6 5 4 3 2 1 0

For Accesory decoders the main CV used are:

CV513Decoder Address (low byte)
Address is between 1 y 511 and controls four outputs (2044 in total)
CV514Auxiliary Activation (a 1 in a bit actives corresponding output)
CV515-CV518Output activation time
CV519Decoder Version (only read)
CV520Manufactured ID (only read)
CV521Decoder address (high byte)

For a complete description of all CV see RP.9.2.2, for programming modes see RP.9.2.3 of NMRA standars.