Uhlenbrock 63120 USB-LocoNet interface

Reference for the Uhlenbrock USB-LocoNet interface (art. 63120) in the context of the BigFred hub. Manufacturer handbook: Bes63120e.pdf (English).

Product page: Uhlenbrock I000C6F6-001.

BigFred terminology: command station / centralka — see 00-terminology.md.

1. Role in BigFred

The 63120 is a USB ↔ LocoNet bridge. Its internal microcontroller handles LocoNet bit timing on the wire; the Pi host sees a USB serial port carrying LocoNet frames. BigFred uses it on the Digikeijs DR5000 path:

loco-server / dcc-bus ──► /dev/loconet-63120 @ 57600 8N1
                              │
                         Uhlenbrock 63120 (USB)
                              │
                         RJ12 ──► command station LocoNet-T (e.g. DR5000)

The 63120 does not replace the command station — it is a throttle-class LocoNet node whose host process is dcc-bus. It is not used with RailBOX RB1110 (use z21 on LAN instead).

Deep-dive on wiring, udev, and frame loss: hardware/04-uhlenbrock-63120.md.

2. Product variants

LocoNet-Tool is required to program LNCV values on the interface itself (§5) and to configure Uhlenbrock LocoNet modules (feedback, switches, LISSY, …).

3. Characteristics (manufacturer)

From the Uhlenbrock handbook:

3.1 Compatible command stations (handbook)

The interface connects LocoNet-capable centrals without a built-in PC port, including:

BigFred official path: Digikeijs DR5000 on LocoNet-T. Other LocoNet masters may work best-effort.

Limitation (manufacturer): feedback from s88 modules wired through Märklin Memory/Interface units cannot be forwarded to the PC through this interface.

3.2 Supported PC software (handbook)

Any program supporting the LocoNet protocol for layout control — e.g. iTrain, RocRail, Koploper, TrainController, DecoderPro, WinDigipet, JMRI (63120Adapter since 4.21.4).

LocoNet-Tool registration: for use with Intellibox, Twin-Center, or PIKO Power Box, register serial numbers at uhlenbrock.de (LocoNet-Tool requirement).

4. Operating modes

The 63120 has two USB↔LocoNet modes, selected by LNCV 4:

Mode (b) in the handbook overview matches LNCV 4 = 0; mode (a) matches LNCV 4 = 1 (direct bytes; handbook ties direct transfer to 19200 in §6).

BigFred requires LNCV 4 = 1 (LocoNet Direktmodus) so dcc-bus receives raw LocoNet frames (opcode … checksum), not a filtered subset.

5. LNCV configuration

Program while the module is on a powered LocoNet bus (command station on), using LocoNet-Tool, a LocoNet throttle with LNCV programming (handbook: “configure by the Intellibox using LocoNet programming”), or rb lncv on Linux.

Reference also: LocoNet-over-TCP interface comparison.

Wrong LNCV 2 or LNCV 4 produces garbage, missing frames, or checksum errors in dcc-bus logs — not a Pi defect.

5.1 rb lncv (Linux alternative to LocoNet-Tool)

BigFred ships rb lncv get and rb lncv set for Uhlenbrock-class LNCV modules. Message format matches JMRI LncvMessageContents; implementation: lncv.go.

Before any command: LocoNet LED must flash on activity (not solid red). Command station on; 63120 on LocoNet data port (DR5000: LocoNet-T).

# Verify bus + module (factory USB baud 115200)
rb lncv get --device /dev/ttyUSB0 --baud 115200 --article 63120 --addr 1 0

# Self-config: Direktmodus + 57600 (use --self-config — no LACK on wire)
rb lncv set --self-config --device /dev/ttyUSB0 --baud 115200 --article 63120 4 1
rb lncv set --self-config --device /dev/ttyUSB0 --baud 115200 --article 63120 2 3

# Verify at new baud
rb lncv get --device /dev/ttyUSB0 --baud 57600 --article 63120 2
rb lncv get --device /dev/ttyUSB0 --baud 57600 --article 63120 4

Full flag list and troubleshooting: hardware/04-uhlenbrock-63120.md §4.2.1.

Self-configuration behaviour: when CV2 (baud) or CV4 (mode) is written, the 63120 applies the change internally and may not echo or acknowledge the write frame on USB. rb lncv treats a confirmed-live programming session plus --self-config as “sent, reconnect to verify”. A power-cycle may be needed if the adapter stops responding after a partial session.

JMRI note: the 63120's own options are documented as safest to configure from a LocoNet throttle on the bus; USB-side programming can briefly drop contact during configuration.

6. LED indicators

7. Physical installation

7.1 Cabling

Command station LocoNet-T ── RJ12 ── [optional 62280 Luisa] ── RJ12 ── 63120 ── USB ── Pi

Pinout and topology: hardware/02-loconet-electrical.md.

7.2 Driver and Linux (BigFred host)

On Linux (Raspberry Pi 5 hub image), the device typically enumerates as a USB serial port (/dev/ttyACM*) — often via the kernel cdc_acm or a USB-UART bridge driver, depending on hardware revision. No Uhlenbrock Windows installer is required.

Install driver before first USB plug-in (handbook) — on Linux, verify with dmesg after connect.

Pin a stable device path with udev (example placeholders — read VID/PID from your unit):

udevadm info -a -n /dev/ttyACM0 | grep -E '{idVendor}|{idProduct}|{serial}'

# /etc/udev/rules.d/99-uhlenbrock-63120.rules
SUBSYSTEM=="tty", ATTRS{idVendor}=="xxxx", ATTRS{idProduct}=="yyyy", \
  SYMLINK+="loconet-63120", GROUP="dialout", MODE="0660"

Add the dcc-bus service user to group dialout. Hub image: bake the rule into the Buildroot overlay (hardware/03-host-platform.md §3.5).

Use a short USB 3 cable to the Pi; avoid sharing the port with other high-bandwidth devices during bring-up.

8. PC ↔ LocoNet protocol (handbook §5)

Uhlenbrock documents an expert-level host protocol for reliable communication:

1. Send over USB, then wait to receive the same message echoed from LocoNet before sending the next message.
2. Process other received messages while waiting.
3. LACK (Long Acknowledge) handling: for messages that can be followed by LACK, set a flag after send/receive; if the next message is LACK, process it as the response; otherwise clear the flag.
4. Do not rely on fire-and-forget sends without flow control — causes errors, especially at 115200 baud where flow control cannot slow the link.

BigFred's loconet.go driver implements LocoNet request/response sequencing and checksum validation on the serial stream. Configure the 63120 for transparent raw frames (§5) so observations from other throttles on the bus reach dcc-bus.

9. BigFred integration

9.1 Protocol contract

loconet_serial expects:

1. 57600 8N1 (8 data bits, no parity, 1 stop bit).
2. Raw bytes per LocoNet message (opcode through checksum inclusive).
3. No ASCII SEND / RECEIVE lines (that is loconet_tcp / LBServer).

Checksum: XOR of all bytes including checksum byte = 0xFF (loconet_proto.go). Example idle frame: 83 7C.

9.2 Catalogue and daemon

Example CLI:

dcc-bus \
  --station-kind loconet_serial \
  --station-uri "serial:///dev/loconet-63120:57600" \
  --speed-steps 128 \
  …

9.3 Capabilities over LocoNet (via 63120)

External observation: 16-dcc-bus/09-external-state-observation.md.

10. LocoNet-Tool (bundled software)

LocoNet-Tool (art. 63120) provides:

• LNCV programming for Uhlenbrock LocoNet modules (feedback, switches, displays, LISSY).
• LocoNet Monitor — watch and analyse bus traffic (useful when debugging LNCV or automatic layout logic).

Configure the 63120's own LNCVs here (§5) while connected to a powered LocoNet segment. On Windows-only workshop PCs this is the supported path.

On Linux, use rb lncv (§5.1) as the primary alternative. Fallbacks: LocoNet-Tool under Wine, a Windows VM, or programming from a LocoNet throttle per handbook.

11. Bring-up checklist

• [ ] 63120 on LocoNet-T (DR5000); central powered; LocoNet LED blinks on activity (not solid).
• [ ] LNCV 2 = 3 (57600), LNCV 4 = 1 (Direct mode) verified (rb lncv get or LocoNet-Tool).
• [ ] USB connected to Pi; /dev/loconet-63120 (or ttyACM*) present; user in dialout.
• [ ] No other program holds the serial port (JMRI, minicom, LocoNet-Tool on same path).
• [ ] BigFred catalogue: loconet_serial, URI serial:///dev/loconet-63120:57600.
• [ ] dcc-bus log: no sustained bad checksum / timeout waiting for slot.
• [ ] setSpeed moves a loco; second browser session on another address works.
• [ ] Handheld change on LocoNet visible in web UI.

Common issues: factory defaults (115200 + filtered mode), wrong LocoNet port (B vs T), solid LocoNet LED (no bus traffic), weak bus power (add 62280), parallel serial port users, USB autosuspend, adapter left in LNCV programming mode (power-cycle USB + LocoNet, then always close session — rb lncv sends prog-end automatically).

Optional sanity check (hardware/06-bringup §6.3):

stty -F /dev/loconet-63120 57600 cs8 -cstopb -parenb raw
timeout 5 xxd /dev/loconet-63120

12. Related documents

Back to the devices index.