CAN Bus Settings Guide

This guide explains how to configure the CAN bus channels in Helix, including quick access controls for common settings and detailed configuration options for advanced timing parameters.

Overview

Helix supports two CAN bus channels (CH1 and CH2) with full configuration capabilities including:

Standard CAN and CAN FD modes
Configurable bitrates from 100 kbps to 1 Mbps (nominal) and up to 8 Mbps (FD data)
Silent (listen-only) mode for passive monitoring
Advanced bit timing configuration for precise sample point control
Automatic bus recovery with configurable restart delays

CAN Quick Access Dropdown

The CAN Quick Access dropdown provides fast access to the most commonly used CAN settings directly from the toolbar, without navigating to the settings pages.

Opening the Dropdown

Click the CAN bus icon in the toolbar to open the quick access dropdown. The icon displays:

Green color when at least one channel is active (bus on)
Muted color when all channels are inactive
Badge number showing the count of active channels (1 or 2)

CAN Quick Access dropdown expanded showing both channels with their settings

Dropdown Layout

The dropdown is organized into the following sections:

Status Header

Displays "CAN Bus" with a count of active channels (e.g., "1/2 active"). A colored accent bar at the top indicates overall status:

Green bar: At least one channel active
Gray bar: All channels inactive

Channel Controls

Each channel (CH1 and CH2) displays:

Status indicator: Green dot when bus is on, gray when off
Channel name: CH1 or CH2
Current bitrate: Displayed in compact format (e.g., "500k", "1M")
FD badge: Shows "FD" with data bitrate when CAN FD is enabled
Silent badge: Shows "Silent" when silent mode is enabled
On/Off button: Toggle to start or stop the bus

Channel row showing CH1 active at 500k with FD 2M enabled

Configuring Settings (Bus Off Only)

When the bus is off, additional configuration options appear:

Baudrate Selection

A row of preset buttons for common bitrates:

Button	Bitrate
100k	100,000 bps
125k	125,000 bps
250k	250,000 bps
500k	500,000 bps
1M	1,000,000 bps

Click a button to select that bitrate. The active selection is highlighted.

Baudrate selection pills with 500k highlighted

CAN FD and Silent Mode

FD checkbox: Enable CAN FD (Flexible Data-rate) for higher data throughput
Silent checkbox: Enable listen-only mode (no transmissions)

When FD is enabled, additional data baudrate options appear:

Button	Data Bitrate
1M	1,000,000 bps
2M	2,000,000 bps
4M	4,000,000 bps
8M	8,000,000 bps

FD enabled with data baudrate options showing 2M selected

All Settings Link

Click "All settings" at the bottom of the dropdown to navigate to the full CAN Settings page for advanced configuration.

Important Notes

Settings apply on bus start: Changes made in the dropdown are applied when you turn the bus on
Real-time status: The dropdown shows actual bus status from system stats when available
Automatic refresh: Status is refreshed each time you open the dropdown

CAN Settings Overview Page

Navigate to Settings > CAN to access the CAN settings overview page.

CAN Settings overview page showing both channels as cards

Channel List

The overview displays all available channels as clickable cards. Each card shows:

Channel number: Large number on the left (green when active, gray when inactive)
Channel name: "Channel 1" or "Channel 2"
Current configuration: Nominal bitrate, and FD data bitrate if enabled
Status badge: "Active" (green) or "Inactive" (gray)

Click a channel card to access its detailed settings.

Status Information

The page displays a helpful note at the bottom:

Changes to CAN settings require the bus to be inactive. Stop the bus before applying configuration changes.

Channel Settings Page

Click on a channel from the overview page to access its detailed settings at /settings/can/1 or /settings/can/2.

Channel 1 settings page header showing channel name, clock speed, and bus status

Page Header

The header displays:

Channel name: "Channel 1 Settings" or "Channel 2 Settings"
Clock speed: The CAN controller clock in MHz (e.g., "80 MHz")
Bus status badge: "Bus Active" (green) or "Bus Inactive" (gray)

Bus Mode Section

Configure the basic operating mode of the CAN channel.

Bus Mode section with three checkboxes

Power on bus state

When enabled, the channel automatically goes bus-on when the device powers up. This is useful for devices that should start monitoring immediately.

Silent mode

When enabled, the channel operates in listen-only mode:

Receives all CAN frames on the bus
Does not transmit any frames (including ACK bits)
Does not affect bus timing
Useful for passive monitoring or when connecting to a bus that already has active participants

Enable CAN FD

When enabled, the channel uses CAN FD (Flexible Data-rate) protocol:

Allows larger payloads (up to 64 bytes vs. 8 bytes for classic CAN)
Supports higher data rates for the payload portion
Requires all bus participants to support CAN FD
Shows additional data bitrate configuration options

Current Configuration Section

Displays the currently configured timing parameters as calculated values.

Current Configuration section showing bitrate and sample point values

Field	Description
Nominal Bitrate	The arbitration phase bitrate (all CAN frames)
Nominal Sample Point	The percentage position where bit sampling occurs
Data Bitrate (FD)	The data phase bitrate (CAN FD only)
Data Sample Point (FD)	Sample point for the data phase (CAN FD only)

The sample point is a critical CAN parameter that determines when the bus state is sampled during each bit period. Typical values are 75-87.5%.

Bitrate Configuration Section

Configure the channel bitrate using either simple or advanced mode.

Mode Toggle

Use the "Advanced" toggle in the section header to switch between:

Simple mode (default): Use sliders to select from preset bitrates
Advanced mode: Fine-tune individual timing segments

Bitrate Configuration section header with Advanced toggle

Simple Mode

In simple mode, use sliders to select from preset values:

Nominal Bitrate Slider

Nominal bitrate slider with tick marks from 100k to 1M

Position	Bitrate
1	100 kbps
2	125 kbps
3	250 kbps
4	500 kbps
5	1 Mbps

Data Bitrate Slider (when CAN FD enabled)

Data bitrate slider with tick marks from 1M to 8M

Position	Bitrate
1	1 Mbps
2	2 Mbps
3	4 Mbps
4	8 Mbps

Advanced Mode

Advanced mode provides direct control over CAN bit timing segments. This is useful when you need precise control over the sample point or when interfacing with systems that require specific timing parameters.

Advanced mode showing Nominal Bitrate timing parameters with sliders

Nominal Bitrate Parameters

Parameter	Description
Propagation Segment	Compensates for signal propagation delays on the bus
Phase Segment 1	May be lengthened during resynchronization
Phase Segment 2	May be shortened during resynchronization
Sync Jump Width (SJW)	Maximum adjustment for resynchronization
Bit Rate Prescaler (BRP)	Divides the clock to achieve the desired bit time

The total bit time (in time quanta) = Sync Segment (1) + Propagation Segment + Phase Segment 1 + Phase Segment 2

Data Bitrate Parameters (when CAN FD enabled)

Advanced mode showing Data Bitrate timing parameters

When CAN FD is enabled, a separate set of timing parameters appears for the data phase:

Parameter	Description
Propagation Segment	Data phase propagation compensation
Phase Segment 1	Data phase segment 1
Phase Segment 2	Data phase segment 2
Sync Jump Width (SJW)	Data phase resynchronization jump width
Bit Rate Prescaler (BRP)	Data phase clock prescaler

Each parameter shows its current value and has min/max limits based on hardware capabilities.

Error Handling Section

Configure how the channel responds to bus errors.

Error Handling section with checkbox and restart delay slider

Bus error reporting

When enabled, bus errors are reported to the application. This allows software to detect and respond to communication problems such as:

CRC errors
Bit stuffing errors
Form errors
ACK errors

Bus restart delay

Configures automatic recovery after the channel enters bus-off state due to excessive errors.

Bus restart delay slider with tick marks

Setting	Description
Off	No automatic restart; manual intervention required
10ms - 100s	Automatically attempt to restart after the specified delay

Available delays: Off, 10ms, 50ms, 100ms, 250ms, 500ms, 1s, 2s, 5s, 10s, 100s

A shorter delay means faster recovery but may cause repeated error bursts if the underlying problem persists. A longer delay gives more time for transient issues to resolve.

Applying Changes

Action buttons (Reload and Apply) at the bottom of the page

Reload Button

Click "Reload" to discard any unsaved changes and refresh settings from the device.

Apply Button

Click "Apply" to save and apply the current settings to the channel.

Important: Settings can only be applied when the bus is inactive. If the bus is active, a warning modal appears:

Bus Active warning modal

Cannot apply CAN channel changes while the bus is active. Please stop the bus first, then try again.

After successful application, a green success message appears:

Settings applied successfully

Status Messages

The page displays contextual feedback:

Success message (green): "Settings applied successfully" - shown for 3 seconds after apply
Error message (red): Displays the error description if apply fails
Warning text (orange): "The bus is currently active. Stop the bus before applying changes." - shown when bus is active

Workflow Examples

Quick Bus Configuration

Click the CAN bus icon in the toolbar
Select your desired baudrate (e.g., "500k")
Enable FD if needed and select data baudrate
Enable Silent if you only want to monitor
Click "On" to start the bus

Precise Timing Configuration

Navigate to Settings > CAN > Channel 1
Turn off the bus if it's active (use Quick Access or settings page)
Enable the "Advanced" toggle
Adjust timing segments to achieve desired sample point
Monitor the "Current Configuration" section for calculated values
Click "Apply" to save settings
Turn the bus back on

Passive Monitoring Setup

Open the CAN Quick Access dropdown
Select your baudrate to match the bus you're connecting to
Check the "Silent" checkbox
Click "On" to start listening without affecting the bus

Troubleshooting

Bus won't go on

Check physical connections to the CAN bus
Verify baudrate matches other devices on the bus
Ensure at least one other device is providing termination
Check for CAN FD mismatch (all devices must support FD if enabled)

Frequent bus-off errors

Check for wiring issues or loose connections
Verify sample point is appropriate for bus length and speed
Consider increasing bus restart delay to allow transient issues to clear
Enable bus error reporting to diagnose specific error types

Settings won't apply

Ensure the bus is stopped before applying changes
Check for hardware/firmware errors in the error message
Try clicking "Reload" to refresh the current state

No data received in silent mode

Verify the bus has active transmitters
Check that baudrate exactly matches other devices
Confirm physical connection to both CAN-H and CAN-L