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)
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
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.
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 |
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.
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.
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.
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.
| 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
Simple Mode
In simple mode, use sliders to select from preset values:
Nominal Bitrate Slider
| Position | Bitrate |
|---|---|
| 1 | 100 kbps |
| 2 | 125 kbps |
| 3 | 250 kbps |
| 4 | 500 kbps |
| 5 | 1 Mbps |
Data Bitrate Slider (when CAN FD enabled)
| 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.
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)
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.
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.
| 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
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:
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
Related Documentation
- Dashboard - Dashboard overview and data visualization
- Settings Overview - All device and application settings
- Getting Started - Platform overview and quick start