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CV Programming Tips

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Hints and Tips

General Programming Best Practices

  1. Use a Dedicated Programming Track (PROG): Always test new or unknown decoders on the dedicated PROG track output of your EX-CommandStation rather than the main track (MAIN) to prevent unintended programming of other locomotives.

  2. Verify Acknowledgement (ACK): Decoder CV reading relies on current-sensing pulses (ACK). If CV reading fails or returns -1 / errors, check physical track contact and wheel cleanliness.

  3. Resetting to Factory Defaults: Most, but not all, DCC decoders (including Hornby) can be reset to factory default settings by writing 8 to CV8. Power cycle the track after issuing a reset command.
    Refer to your decoder manual to confirm that this is to correct way to reset it.

Hornby HM7000 decoders

The HM7000's DCC implementation has a bug in that the ACK response to a DCC CV read from the decoder on the programming track is far, far too long. So much so, the DCC-EX developers added a feature to cater specifically for the HM7000.

Dual-Mode Operation

Hornby HM7000 decoders can operate in both Bluetooth (BLE) mode via the Hornby HM | DCC app and standard DCC mode. When connected active to Bluetooth, DCC programming commands from your EX-CommandStation may be ignored or rejected.

  • Unlink/Disconnect Bluetooth for DCC Programming:
    To reliably read or write CVs over the DCC programming track (PROG) or main track (POM) with EX-CommandStation, ensure the decoder is not actively connected to the Hornby HM | DCC app on your mobile device. Close the app or disconnect the locomotive in the app before attempting DCC CV programming.
  • Make sure the loco is on the PROG output which is typically channel B on the EX-CommandStation.
  • Bring up a serial console to the EX-CommandStation, or use the command entry features in EX-Toolbox, EX-WebThrottle or Engine Driver.
  • Type and send <1 PROG> to force the PROG track to power up early.
  • Type and send <D ACK MAX 20000>
  • Then try reading the decoder.
    Either from the console with ,
    or with the appropriate buttons in EX-Toolbox, EX-WebThrottle or Engine Driver,
    to watch for a response.
  • If this isn't working, then also add <D ACK MIN 150>

If this isn't working, then <D ACK ON> will enable diagnostic output from the EX-CSB1 to show what the is doing.

Additional Notes

  • Power Cycle After Programming:

    After updating CVs on an HM7000 decoder via DCC, perform a full power cycle (turn track power off and back on via your throttle or EX-WebThrottle) to ensure the decoder reloads and applies the new CV settings properly.

  • ACK / Current Pulse Sensing:

    HM7000 sound decoders can draw higher current bursts during startup or acknowledgment pulses. If you experience ACK read timeouts during PROG track operations:

    • Ensure the programming track rails and locomotive wheels are clean.
    • Verify that track power limits on your EX-CommandStation motor shield are configured correctly for standard DCC acknowledgment pulses.

  • You can also refer to the RailSnail -DCC-EX and Hornby TTS Decoders – (No ACK!) article for more information.

Hornby Bluetooth Firmware Updates

Always use the official Hornby HM | DCC app via Bluetooth to update the HM7000 decoder firmware to the latest release before configuring custom DCC CV settings.

Making the changes permanent

If you expect to be needing this often, you can add whatever commands you found worked for you, to your myAutomation.h. e.g.

AUTOSTART
  PARSE("<D ACK MAX 20000>")
  PARSE("<D ACK MIN 150>")
DONE