How to set CV29: direction, speed steps, analogue and long address
Decode the bits of CV29, the decoder's main configuration register, and build the right value for direction, 28/128 speed steps, DC running, RailCom and long addressing.
- Time
- 15 minutes
- Difficulty
- Medium
- Cost
- No extra cost
- Steps
- 5
- Checked
What you’ll need
- Your command station or JMRI DecoderPro
- The decoder manual
- Optional: the CV29 builder on this site
Before you start
- Don't set bit 7 on a loco decoder – it marks the decoder as an accessory decoder.
Step by step
-
Step 1: Know what each bit does
CV29 bits and their values (NMRA S-9.2.2, ESU LokPilot 5): - Bit 0 (1) – reverse the loco's normal direction (lights follow) - Bit 1 (2) – 28/128 speed steps on; 0 = 14 steps - Bit 2 (4) – allow analogue (DC) running - Bit 3 (8) – RailCom (bi-directional communication) on - Bit 4 (16) – use the custom speed table CV67–94 instead of CV2/5/6 - Bit 5 (32) – use the long address in CV17/18 - Bit 6 (64) – reserved - Bit 7 (128) – accessory decoder (not for locos)
Next: step 2 -
Step 2: Read the current value
Read CV29 on the programming track. ESU LokPilot 5 decoders come set to 12 (analogue + RailCom), for example; other makes differ.
Next: step 3 -
Step 3: Add up the bits you want
Add the values of every bit you want switched on. For example: 28/128 steps (2) + analogue running (4) + long address (32) = 38. Without analogue: 2 + 32 = 34.
Next: step 4 -
Step 4: Write the new value
Write it on the programming track or on the main (if your system supports POM for CV29). Then test.
Next: step 5 -
Step 5: Check the loco behaves
Loco won't respond properly? Digitrax lists a mismatch between CV29 and the command station's speed-step mode as a cause – check bit 1. Loco runs backwards? Toggle bit 0.
Tips
- The NMRA's 2012 wording describes bit 1 in terms of which packet controls the headlight; decoder makers describe the same bit as the 14/28-step setting.
Questions people ask
My command station sets CV29 for me – should I touch it?
If its long-address menu works, let it. Use this guide when you need to change direction, DC running or RailCom.
Why doesn't my value stick?
The NMRA says decoders shouldn't let unsupported bits be set, so a decoder may ignore bits for features it lacks.
Sources
Checked 18 October 2026. We wrote this guide in our own words, using:
- NMRA S-9.2.2 Configuration Variables (July 2012) (nmra.org)
- ESU LokPilot 5 instruction manual, Edition 7 (distributor copy) (intermountain-railway.com)
- Digitrax DCS240 command station manual (digitrax.com)
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Printed from dcctrainautomation.uk/guides/set-cv29-correctly/ · Checked 18 October 2026 · General information only. Follow the maker’s instructions for your own equipment, and keep mains wiring inside properly made, enclosed power supplies.