CANBUS
The 305ap has two independent FDCAN ports supporting DroneCAN (formerly UAVCAN v1/v0) peripherals.
Hardware
| Port | TX | RX | Enable (STB) | Transceiver |
|---|---|---|---|---|
| FDCAN1 | PD1 | PD0 | PA10 (active-low) | SIT1044T/K/3 |
| FDCAN2 | PB6 | PB5 | PE1 (active-low) | SIT1044T/K/3 |
The STB (standby) pin controls the CAN transceiver: low = normal operation, high = standby. The firmware drives both STB pins low at boot, so the transceivers are always active.
PA10 note: PA10 was repurposed from USART1 as the FDCAN1 STB line. It is not available as a UART pin.
CAN Transceivers
Both CAN ports use SIT1044T/K/3 transceivers, which are ISO 11898-2:2016 compliant CAN FD transceivers rated to 5 Mbps. Key features:
- 3.3 V / 5 V MCU I/O compatible
- Standby mode (controlled by STB pin)
- Undervoltage protection
- TX dominant timeout
- Thermal shutdown
- Unpowered-node bus disengagement (does not corrupt the bus when unpowered)
Wiring
CAN uses a differential pair. Connect:
- CAN H to CAN H
- CAN L to CAN L
- GND to GND
The 305ap includes two 120 Ω termination resistors onboard for each CAN port. The bus is fully terminated at the FC. Do not add any external termination resistors on the cable run or at peripheral devices — extra resistors will lower the bus impedance below the ISO 11898-2 spec and degrade signal integrity.
Do not wire CAN as a star. Run a single bus from the FC through each device in a line (daisy chain).
Enabling DroneCAN in PX4
- In QGC → Parameters, set
UAVCAN_ENABLE= Sensors Automatic Config (2) or higher - Reboot
- PX4 will enumerate all DroneCAN devices on the bus and configure them automatically
UAVCAN_ENABLE covers both ports; devices can be on either. See DroneCAN for sensor subscriptions and ESC setup.
Common DroneCAN Peripherals
| Device type | Examples |
|---|---|
| ESCs | Myxa, Zubax Kotleta20, Flame |
| GPS | Zubax GNSS, Holybro M9N DroneCAN |
| Airspeed | Zubax Baro, SDP3x via DroneCAN |
| Power monitor | Zubax Power, Pomegranate Systems |
Troubleshooting
In the MAVLink Console:
uavcan status
Lists all enumerated DroneCAN nodes with their node IDs and health status.