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CAN Bus, DBC & ARXML: The Formats Behind Automotive Network Data

Behind every CAN frame lies a precise structure — defined by a DBC or ARXML file your tool needs to parse without choking. Here is what these formats actually contain.

Every vehicle built in the last 30 years runs on a network of ECUs that communicate over CAN. But raw CAN frames — a header, a few bytes of data — tell you nothing without a database that describes what those bytes mean. That database is your DBC or ARXML file.

What's in a DBC file

DBC (Database CAN) is the format originally developed by Vector Informatik. It is a plain-text file that describes:

  • Messages (frames): ID in decimal or hex, DLC, sending node, cycle time
  • Signals: start bit, bit length, byte order (Intel or Motorola), value type (signed/unsigned), factor, offset, unit, min/max
  • Value tables (VAL_): enumerations — e.g. 0=Off, 1=Slow, 2=Fast
  • Attributes (BA_DEF_ / BA_): custom metadata attached to the database, messages, or signals
  • Nodes: ECUs present on the bus
  • Comments (CM_): descriptions attached to messages, signals, or nodes

A simple DBC message looks like this:

BO_ 256 EngineData: 8 Engine_ECU
 SG_ EngineSpeed : 0|16@1+ (0.25,0) [0|16383.75] "rpm" Vector__XXX
 SG_ ThrottlePos : 16|8@1+ (0.392157,0) [0|100] "%" Vector__XXX

This tells you: message ID 256 (0x100), 8 bytes, sent by Engine_ECU. Signal EngineSpeed starts at bit 0, is 16 bits wide, Intel byte order, unsigned, scale factor 0.25, no offset, range 0–16383.75 rpm.

CAN FD and extended multiplexing

Modern DBC files also handle CAN FD (DLC up to 64 bytes) and extended multiplexing via SG_MUL_VAL_. Standard multiplexing uses a mux indicator signal; extended multiplexing allows ranges, making it possible to have hundreds of logical signals in a single frame.

ARXML: AUTOSAR's answer

ARXML (AUTOSAR XML) goes further. Where DBC is a flat description of bus traffic, ARXML is a hierarchical model of the entire communication architecture:

  • Software components and their interfaces
  • PDUs (Protocol Data Units) that map to signals
  • I-Signals with their data transformers
  • Cluster and channel configuration for CAN, FlexRay, Ethernet
  • ECU instances with their COM mappings

AUTOSAR 4.x added E2E (End-to-End) protection profiles (P01 through P07) and SecOC (Secure Onboard Communication) with AES-128-CMAC or HMAC-SHA256. K-Matrix Studio parses and displays these protection layers. ARXML 3.x, used in older projects, has a different namespace and structure — K-Matrix Studio auto-detects the version.

FIBEX: for FlexRay

ASAM's FIBEX format (Field Bus Exchange Format) describes FlexRay, CAN, and LIN networks in XML. It is common in Tier 1 workflows for FlexRay-based systems. FIBEX files can be either `.fibex` or `.xml`. K-Matrix Studio renders a dedicated FlexRay timeline view with 64 cycles, distinguishing static and dynamic segments.

What this means in practice

If your tool cannot parse CAN FD DLC, extended multiplexing, or AUTOSAR E2E attributes, you are working with an incomplete picture of the bus. K-Matrix Studio parses all of these, shows them in a unified interface, and never asks for a license key.

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