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Yes—a Raspberry Pi Pico can communicate on a CAN bus using Kevin O’Connor’s open-source can2040 library, but the Pico cannot connect directly to CANH and CANL. The library implements the CAN controller functions in software and RP2040/RP2350 PIO; you still need an external CAN transceiver, correctly wired bus, termination, and another active CAN node. The project documents CAN 2.0B data frames at rates up to 1 Mbit/s.
What can2040 does—and what it does not
Many microcontrollers have a dedicated CAN controller peripheral. The RP2040 does not, so can2040 uses the chip’s Programmable I/O (PIO) hardware and software to implement CAN controller behavior. Kevin O’Connor’s project supports Raspberry Pi RP2040 and RP2350 microcontrollers and documents CAN 2.0B data frames up to 1 Mbit/s.
That makes can2040 a controller implementation, not a complete electrical CAN interface. The Pico’s GPIO signals are not the differential CANH/CANL bus signals. An external transceiver is required to convert between them; connecting Pico GPIO directly to CANH or CANL is not a substitute.
How PIO handles CAN
The implementation uses one PIO block and all four of that block’s state machines. PIO runs timing-sensitive operations alongside the ARM core, which reduces the amount of protocol work the CPU must handle directly.
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- One state machine handles synchronization and bit sampling.
- Another transfers received data through the receive FIFO.
- Another handles CRC and acknowledgement matching.
- The transmit state machine sends frames while participating in arbitration and acknowledgement.
CAN arbitration depends on nodes observing the bus while transmitting: a node that sends a recessive bit but observes a dominant one yields to the higher-priority frame. The transmit logic’s participation in this process is important; this is not simply a GPIO routine that sends bytes without regard to other bus traffic.
The project’s pio/can2040.pio source says the implementation is designed to run at 32 times the CAN bitrate. It also notes the PIO program’s 32-instruction limit, which constrains how the logic can be arranged. That internal timing figure is not a claim that the bus itself runs 32 times faster.
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Hardware you need for a working bus
At minimum, the documented test setup needs a functioning CAN transceiver, CANH and CANL wiring, two 120-ohm termination resistors, at least one other CAN-enabled chip, and the same CAN bitrate configured on every node. The can2040 Tools documentation warns that an incomplete physical bus will not work even for debugging.
Choose a transceiver module
A Raspberry Pi Pico paired with a Waveshare SN65HVD230 CAN Board is the example setup named in the project’s Tools documentation. An SN65HVD230 CAN transceiver module is a useful search phrase when looking for that type of hardware. Check the module’s pin labels and electrical requirements against its own documentation and your board; the can2040 software does not make a transceiver unnecessary.
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- Example Projects: Each project has schematics, wiring diagrams, complete code and detailed explanations (Need extra items)
Wire and terminate the bus
- Connect the Pico’s selected CAN RX and TX GPIOs to the corresponding logic-side pins on the transceiver, following the module’s pinout.
- Connect the transceiver’s CANH and CANL pins to the matching bus lines. Do not connect the Pico’s GPIO directly to those bus wires.
- Provide two 120-ohm termination resistors on the physical bus, as specified by the project’s minimum test setup.
- Connect at least one other CAN-enabled device and configure all nodes for the same bitrate.
The project’s API example uses GPIO4 and GPIO5 at 500,000 bit/s. Those are illustrative values, not universal Pico pin requirements or a required bus speed. Select GPIOs that suit your wiring and board, and pass the chosen pins and bitrate to the library.
Integrate can2040 with the Pico SDK
The API guide’s example follows this order. Its GPIO and bitrate values are examples; adapt them to the transceiver wiring and bus you have built.
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- Allocate the controller state. Provide storage for a
struct can2040. - Set up PIO. Call
can2040_setup()and select PIO0 or PIO1. The implementation uses all four state machines in the selected PIO block. - Register callbacks. Use
can2040_callback_config()to register receive, transmit, and error handling. - Connect the PIO interrupt. Enable the PIO IRQ and call
can2040_pio_irq_handler()from the interrupt handler. - Start the bus. Call
can2040_start()with the system clock, CAN bitrate, RX GPIO, and TX GPIO.
Callbacks run in IRQ context. Keep them short: the API guide recommends copying message data for processing later in normal context rather than doing lengthy work in the callback. Receive overflow is reported as CAN2040_NOTIFY_ERROR. The library does not perform receive filtering, so an application that needs to accept only selected messages must filter them itself.
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Although PIO handles timing-sensitive CAN work, the implementation remains sensitive to interrupt latency. The API guide recommends minimizing work in higher-priority interrupts and considering whether can2040 code, callbacks, and vector tables should be placed in RAM.
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The guide notes that on an RP2040 running at 125 MHz, a 32-bit flash load can take at least 320 ns. Flash stalls can therefore affect CAN timing. Treat the library’s documented maximum bus rate as a supported capability, not a guarantee that every application will meet timing under every interrupt, memory, and bus-load condition.
Compatibility, build requirements, and license
- RP2040: The API documentation specifies Pico SDK 1.3.0 or later.
- RP2350: It specifies Pico SDK 2.0.0 or later and the
-DPICO_RP2350compiler flag. - Without the full Pico SDK: The C source files can be built separately, but SDK headers are still needed.
- License: The API documentation identifies the project as GPLv3. Review the license terms for your intended use and distribution.
For Arduino projects, the separate ACAN2040 wrapper offers a higher-level route for RP2040 and RP235x boards, including Pico and Pico W. It still requires an external CAN transceiver.
When to use can2040 instead of a dedicated CAN controller
can2040 is a practical option when you want to use an RP2040 or RP2350 board and are comfortable integrating its C API or an Arduino wrapper. A dedicated CAN-controller solution may be preferable if you want protocol work handled outside the Pico’s PIO and CPU resources, or if your chosen board already integrates the required CAN hardware. Either way, verify what the hardware includes: a controller and a transceiver are different parts of the interface.
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Quick Recap
- Electrical hardware: can2040 needs an external transceiver; some integrated CAN boards may include one.
- Resource and timing budget: can2040 uses one PIO block and requires attention to interrupt latency. Dedicated controllers move protocol work elsewhere.
- Software integration: can2040 provides a Pico SDK C API, with ACAN2040 as an Arduino wrapper option.
- Documented protocol scope: the project specifies CAN 2.0B data frames up to 1 Mbit/s.
- Physical bus validation: correct CANH/CANL connections, two 120-ohm terminations, a second active node, and matching bitrates are part of a functioning setup.
- License and version: the project is GPLv3; check the maintained repository revision and its documentation for the requirements that apply to your build.
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