CV29 Calculator

DCC decoder configuration · CV29

DCC CV29 Calculator

CV29 is eight on/off settings packed into one number. Flip the switches to build the value you need, or type in a value read back from a decoder to see what it is set to. Bit meanings follow NMRA S-9.2.2 for multifunction (locomotive) decoders.

NMRA S-9.2.2 Configuration Variables NMRA S-9.2.1 Extended Addressing CV29 range 0–255

CV29 value (decimal)

Hex0x06

Binary0000 0110

Common settings

What this value does

CV29 = 6

Bit by bit

What each bit controls

Each bit has a fixed weight: 1, 2, 4, 8 and so on. CV29 is the sum of the weights of every bit that is on. Most loco decoders only use bits 0 to 5.

CV1 · CV17 · CV18

Loco address calculator

Bit 5 of CV29 decides which address the decoder answers to. Off uses the short address in CV1. On uses the long address split across CV17 and CV18. Enter either the loco number or the raw CV values; the other side updates.

Long loco address

CV17

CV18

CV1 (short)

How CV17 and CV18 are worked out

CV17 and CV18 are not the first and last two digits of the address. The address is written as a 16-bit binary number, the top two bits are forced to 11, and the result is split into two bytes.

CV17 = 192 + ⌊addr ÷ 256⌋201

CV18 = addr mod 256233

Reference

Common CV29 values

Select a row to load it into the calculator.

Value	Binary	Address	Speed steps	Analogue	Other	Typical use

Read before you write

Read back CV29 before changing it and note the value. If a loco stops responding after a change, you can put the original value straight back.

Short address range

NMRA allows short addresses 1–127 in CV1. Some command stations treat 100 and above as long, so 1–99 is the safest choice for running on any system.

Long address range

NMRA S-9.2.1 allows long addresses 0–10239. Command stations vary in what they accept. Keeping to 128–9983 works on almost every system.

Bit definitions follow NMRA Standard S-9.2.2 (Configuration Variables for Digital Command Control) and S-9.2.1 (Extended Packet Formats). Always check your decoder manual: some manufacturers add their own uses for bits 3, 4, 6 and 7.