Working with the CAN Bus

Applies to: IOcan · Standalone controller. What this means

Several IO types exchange data over CAN. This page covers the shared concepts they depend on; the per-IO pages cover the specifics.

CAN bus definition

Before adding any CAN IO you must have a CAN bus defined, with:

Setting Meaning
CAN ID / bus Which physical CAN channel.
Baud rate Bus speed (e.g. 500 kbit/s).
CAN FD Enable FD and set the FD data baud rate, if used.
Termination Enable the on-board 120 Ω terminator when the controller is an end node.

Two ways to use CAN

1. Raw frame signals

Decode/encode individual CANbus signals directly from raw CAN frames by hand. Use these when you have a DBC or know the byte layout:

  • CAN Bus Input — extract a signal from an incoming frame (message ID, endianness/bitfield, length, offset, scaling, timeout behaviour).
  • CAN Bus Output — pack a signal into an outgoing frame.

2. CAN Presets

CAN Presets are predefined device profiles (dashes, ECUs, shifters, keypads, paddles…) that live in canbusEntities/. A preset publishes/consumes a set of named CAN objects and handles all the byte decoding/encoding for you. When you add a preset it automatically creates the matching object IO — you reference or drive those rather than hand-decoding bytes:

  • CAN Object Input — a preset-created input carrying a named object's value (not configured by hand).
  • CAN Object Output — a named object the preset sends, driven by a source value.

Choosing between them

  • Use raw frame signals for arbitrary/custom devices where you know the layout.
  • Use CAN Presets for supported devices — less error-prone, no manual byte math.

Timeouts (inputs)

CAN inputs define what to report if a frame stops arriving (TimeoutMode):

  • UsePrevious — hold the last received value, indefinitely.
  • UseDefault — substitute the Default value.
  • UseFault — substitute the Fault value. Despite the name it raises no fault; it exists so a dropout can look different from a default.

All three are implemented from firmware 2.1. Set a timeout on any safety-relevant signal so a dropped frame is detected rather than silently held, and note that a timeout of zero means 500 ms rather than "no timeout" — see CAN Bus Input.