CV - Configuration Variables

Each DCC decoder can be programmed to respond to a specific address. Locomotive decoders can also be programmed to use 14, 28 or 128 steps, the value of acceleration or braking, etc. The activation time of the outputs can be changed for accessories. All these properties are stored in certain internal memory positions of the decoder called Configuration Variables or simply CV.

The programming of the CVs is done from the Digital Central in several ways called programming modes (direct, register, page, PoM) not all decoders accept all the programming modes so to program the CVs we must check the programming modes which accepts in the decoder manual, usually Direct mode and PoM (Programming on the Main track).

For a complete description of all CVs see NMRA standard S-9.2.2 and S-9.2.3 for programming modes and RCN-214 for CVs and RCN-216 for programming modes from VHDM.



The main CVs that many decoders of locomotives and functions accept are these:

CV Description
CV1 Address of the decoder (1 - 99 or 1-127 according to systems)
CV2 Minimum starting voltage
CV3 Acceleration timing
CV4 Braking timing
CV5 Maximum speed
CV6 Mid speed
CV7 Decoder version (read only)
CV8 Manufacturer ID (read only)
CV17-CV18 Extended address (1 - 9999). They must be programmed in a special way:

Address
CV17
CV18
CV19 Address for multiple traction
CV29 Decoder configuration
Its value is calculated according to its bits for a given configuration

Bit 0 → 0: 0: Normal direction, 1: Reverse direction
Bit 1 → 0: 14 steps, 1: 28 / 128 steps
Bit 2 → 0: DCC only, 1: DCC and direct current
Bit 3 → 0: RailCom disabled, 1: RailCom enabled
Bit 4 → 0: Factory speed curve (CV2, CV6, CV5), 1: User speed curve (CV66-CV95)
Bit 5 → 0: 0: Address in CV1, 1: Address in CV17-CV18

CV29 7 6 5 4 3 2 1 0






For accessory decoders the main CVs are:

CV (traditional) CV (current) Description
CV513 CV1 Decoder address (low byte)
Traditionally the address is between 1 and 511 and controls four outputs (2044 in total)

Address
CV513
CV521
Outputs
CV514 CV2 Output activation (a 1 in a bit allows the corresponding output to be activated)
CV515-CV518 CV3-CV6 Activation time for outputs
CV519 CV7 Decoder version (read only)
CV520 CV8 Manufacturer ID (read only)
CV521 CV9 Decoder address (high byte)