IOCAN

# Working with the CAN Bus

Several IO types exchange data over CAN. This page covers the shared concepts they

depend on; the per-IO pages cover the specifics.

> Schema: `Canbus`, `CanbusInputFrameDescription`, `CanbusOutputFrameDescription`

> and `CanbusEntityHandler` in `config/Config.proto`; the `canbusEntities/`

> folder holds the predefined **CAN Presets**.

## 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](CAN_Bus_Input)** — extract a signal from an incoming

  frame (message ID, endianness/bitfield, length, offset, scaling, timeout

  behaviour).

- **[CAN Bus Output](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](CAN_Object_Input)** — a preset-created input

  carrying a named object's value (not configured by hand).

- **[CAN Object Output](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`, `UseDefault`, or `UseFault`. Set a timeout for any safety-relevant

signal so a dropped frame is detected rather than silently held.