canbus

Controller Area Network (CAN)

The Controller Area Network, also known as CAN or the CAN Bus, is the infrastructure used for internal networking in modern automobiles. It is controlled through a low level system of controller nodes, each of which broadcast all of their data onto the bus. It is therefore the responsibility of the listener nodes to filter through the noise, and determine what traffic is relevant to their individual needs/purposes.

These nodes communicate with each other in a way that is, for the most part, unreadable and otherwise useless to humans in its raw form. Therefore, a semi-standardized format was developed by Vector GmbH to facilitate interpreting and translating the raw Signal values (from sensors and modules), into human-readable values and units (for gauges and data-loggers).

This is the .dbc format I’ll be focusing on in this repository and its accompanying Wiki.

How are .dbc files created?

Every auto manufacturer has their own proprietary “dictionary” which contains the mappings of their platform’s specific adjustment factors/offsets, labels, and units, used to translate the raw sensor values into meaningful data points.

Sometimes these dictionaries (or “databases”, “documents”) are leaked online, or sold by a disgruntled (former) employee. In most cases, however, enthusiasts such as myself spend countless hours, usually in their own cars, reverse-engineering translations to .dbc files.

This is very much a work in progress.

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DBC Specification

1. VERSION
2. NS_: New Symbols
3. BU_: Board Units
   • Syntax
   • Examples
4. BO_: Messages
   • Syntax
   • Attributes
   • Examples
5. SG_: Signals
   • Syntax
   • Multiplexers
   • Attributes
6. BA_: Attributes
   • Syntax
   • Definitions
   • Defaults
7. CM_: Comments
   • Syntax
   • Syntax (scoped)
   • Board Units
   • Messages
   • Signals
8. VAL_: Values
   • Syntax
   • Examples

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Downloadable .dbc files

Vehicle	File Name	Version	Author
BMW E90	bmw-e90.dbc (raw)	2021.6.8	@nberlette
BMW E39	bmw-e39.dbc (raw)	2021.6.6	translated from .kcd by @kmalinich
Mazda (2017)	mazda_2017.dbc	--	@commaai/opendbc
Lexus RX350	lexus_rx350.dbc	--	@commaai/opendbc
Tesla Model 3	tesla_model3.dbc	2020.40.1	@johnmccalla and @onyx-m2 project
OBD2 (universal)	obd2.dbc (raw .dbc)	0.0.1	csselectronics.com
J1939 (universal)	j1939.dbc (raw .dbc)	7.6	Unknown, from haskell.org

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Resources

• Boilerplate .dbc Template
• CANpy Original DBC Specification
• @commaai/opendbc project - open source DBC project
• @kmalinich/node-bmw-ref - BMW KCAN / KBUS / IBUS reference
• loopybunny.co.uk - BMW K-CAN documentation
• canmatrix - translate .dbc files to other filetypes

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References

• PiSnoop DBC Help
• CAN Format for VBOXII and PRO v4 (pdf)
• J1939 DBC from Haskell.org (dbc)
• CANtool Manual (pdf)