An independent Python client for the Rackbus SL serial protocol — the legacy proprietary fieldbus used by some Endress+Hauser mass flowmeters and other Commutec-family transmitters from the mid-1990s.
This is a clean-room reverse-engineered implementation based on black-box observation of unencrypted traffic on the wire. No vendor firmware was decompiled, no vendor software was modified, no proprietary documentation was reproduced.
Disclaimer. This project is not affiliated with, endorsed by, or sponsored by Endress+Hauser AG. Rackbus, Commubox, Promass, Commutec may be trademarks of their respective owners — used here purely descriptively. The wire-format description in this repository is derived solely from observed traffic on equipment lawfully owned by the author. See NOTICE.md for full legal positioning.
Many Coriolis flowmeters and process instruments from 1995-2003 use the Rackbus SL protocol over RS-485. The vendor's original software (Commuwin II) was discontinued long ago, requires legacy hardware dongles, and runs only on Windows 95/98/XP.
These instruments are still in production use across dairy plants, breweries, chemical facilities, and pharmaceutical lines. Replacing them costs tens of thousands of euros per unit plus weeks of downtime.
This library lets you read live data from such instruments using modern, cheap hardware:
- A $5 USB-to-RS485 adapter and Python — for laptops and gateway PCs
- An ESP32 + MAX485 module — for embedded telemetry, MQTT, Home Assistant
- Any platform with a serial port and an RS-485 transceiver
Read-only by design — you can pull mass flow, density, temperature, totalizers, and tags without risk of accidentally writing wrong configuration to live equipment.
git clone https://github.com/kenjicd/py-rackbus.git
cd py-rackbus
pip install pyserial
python examples/basic_usage.py COM5 3That assumes the instrument is at bus address 3 on COM5. Replace
with whatever you have. Wiring:
Instrument terminal A (or +) ─── USB-RS485 A (D+)
Instrument terminal B (or -) ─── USB-RS485 B (D-)
Instrument shield / ⊥ ─── USB-RS485 GND (optional)
Standard RS-485 polarity. See hardware/README.md for diagrams and tips.
from rackbus_client import RackbusClient
with RackbusClient(port='COM5', address=3) as client:
print(client.read_mass_flow()) # → float (t/h)
print(client.read_density()) # → float (g/cm³)
print(client.read_temperature()) # → float (°C)
print(client.read_totalizer_1()) # → float (t)
print(client.read_tag_number()) # → str
print(client.read_parameter('V0H0')) # generic by V/H code
print(client.read_all()) # → dict of common paramsFull API surface and module layout: docs/STRUCTURE.md.
A working PlatformIO firmware for ESP32-S2 (and any other ESP32 variant)
is included in firmware/. It reads the Promass over
RS-485 via a MAX485 module, serves a local web UI with live values, and
optionally posts JSON telemetry to a remote endpoint.
cd firmware
cp include/secrets.h.example include/secrets.h
$EDITOR include/secrets.h # WiFi, OTA password, telemetry URL
pio run -t upload # first flash over USB
pio device monitor # see live transactionsAfter that you can flash over WiFi (pio run -t upload -e ota) and
open http://promass.local/ in a browser.
See firmware/README.md for the full guide and especially the MAX485 turnaround timing warning — that one will save you hours.
| Component | Status |
|---|---|
| Frame structure (request + response, long + short) | ✅ Fully reversed |
Address encoding (0x5F − ASCII + parity) |
✅ Verified |
V/H encoding (0x5F − raw int + parity) |
✅ Verified |
Data decoding (ASCII complement, scale-char, integers, strings, @ invalid) |
✅ Verified on real values |
| Request checksum | ✅ Reversed (crc1 = 0x2E XOR …, crc2 = sum + 0x48) |
| Response checksum | ⚠ Stub (slave trusted; verifier always returns True) |
| Multi-stage exchange (warmup → VR → DD → 48) | ✅ Reversed and reliable |
| Test suite | ✅ 57 tests passing |
| Confirmed device | Promass 63 (63FS50-FTW91A00B1B, SW 3.00.00) |
| ESP32 firmware port | ✅ Working (firmware/, PlatformIO, MAX485) |
| Modbus TCP gateway | 🚧 Planned |
| Manufacturer | Model | Firmware | Tested | Notes |
|---|---|---|---|---|
| Endress+Hauser | Promass 63 | SW 3.00.00 / SW COM 3.00.00 | ✅ | Reference device |
Likely compatible (untested) — please report:
- Other Endress+Hauser Promass 60-series with RACKBUS RS 485 module
- Other Commutec-family transmitters of the same generation (Promag 50/53, Levelflex, Cerabar) in their Rackbus variants
If you have one on the bench, please file a compatibility report.
- docs/PROTOCOL.md — Wire protocol specification (frame format, encoding, checksum, multi-stage exchange)
- docs/PARAMETERS.md — V/H parameter map for supported instruments
- docs/EXAMPLE_TRANSACTIONS.md — Byte-for-byte capture examples with decoded values
- docs/REVERSE_ENGINEERING.md — How the protocol was figured out, dead ends, lessons learned
- docs/STRUCTURE.md — Code layout and API surface
- hardware/README.md — Wiring diagrams for USB adapters and ESP32
- firmware/README.md — ESP32-S2 firmware (PlatformIO), HTTP/JSON API, telemetry publisher, OTA updates, and a sharp warning about MAX485 turnaround timing
pip install pytest pyserial
pytestExpected output: 57 passed.
The test suite uses byte-for-byte fixtures captured from a real device and runs offline (no hardware needed for tests).
See CONTRIBUTING.md. Particularly welcome:
- Compatibility reports for other Rackbus devices
- Response-CRC reverse engineering (we have the captured material; the formula isn't found yet)
- ESP32 / Arduino / STM32 ports
- Wireshark dissector
- Modbus TCP gateway
MIT — see LICENSE. All code in this repository is original work by the contributors and is not derived from any proprietary source.
For the legal positioning of the reverse-engineering effort itself (EU Software Directive 2009/24/EC, US 17 USC § 1201(f), trademark notes), see NOTICE.md.
This library is intentionally read-only. Write operations to live industrial process instruments can cause equipment damage, process upsets, or safety incidents. Always test on a bench setup before connecting to a production line.
