The Feather M4 CAN Express is loaded with microcontroller and CAN goodness. It also has many pins and ports. Let's take a tour!

If you've used the Feather M4 (non-CAN version) - please note that the pinouts for the CAN version use the same exact GPIO's for all exposed pins. This makes the CAN Feather M4 work with all of the GPIO-specific accessories like RGB matrix drivers, NeoPXL8 wings, etc.

Power

  • USB C port - This is used for both powering and programming the board. You can power it with any USB C cable and will request 5V from a USB C PD. When USB is plugged in it will charge the Lipoly battery.
  • GND - this is the common ground for all power and logic
  • BAT - this is the positive voltage to/from the JST jack for the optional Lipoly battery
  • USB - this is the positive voltage to/from the USB C jack if connected
  • EN - this is the 3.3V regulator's enable pin. It's pulled up, so connect to ground to disable the 3.3V regulator
  • 3V - this is the output from the 3.3V regulator, it can supply 500mA peak

CAN Bus

The SAMDE51 has built in hardware CAN bus support, but you still need a transceiver.

We use a 3V-logic compatible transceiver (the 8-SOIC chip).

Right above it, there is a small 3V->5V switched-capacitor boost converter so that the output CAN signals are +-5V.

By default both the boost converter and the transceiver are disabled. The boost-enable pin is connected to pin #4 (BOOST_ENABLE in CircuitPython), and the transceiver enable (standby) is on a pin named PIN_CAN_STANDBY

Here is Arduino code to turn on both the transceiver and booster:

pinMode(PIN_CAN_STANDBY, OUTPUT);
digitalWrite(PIN_CAN_STANDBY, false); // turn off STANDBY
pinMode(4, OUTPUT);
digitalWrite(4, true); // turn on booster

In CircuitPython you can use this snippet to enable

# If the CAN transceiver has a standby pin, bring it out of standby mode
if hasattr(board, 'CAN_STANDBY'):
    standby = digitalio.DigitalInOut(board.CAN_STANDBY)
    standby.switch_to_output(False)
 
# If the CAN transceiver is powered by a boost converter, turn on its supply
if hasattr(board, 'BOOST_ENABLE'):
    boost_enable = digitalio.DigitalInOut(board.BOOST_ENABLE)
    boost_enable.switch_to_output(True)

The board has a 120 ohm terminator connected between H and L. You can disable (remove) the terminator by cutting the Trm jumper, if your bus is already terminated!

Logic Pins

This is the general purpose I/O pin set for the microcontroller.
All logic is 3.3V
Nearly all pins can do PWM output
All pins can be interrupt inputs

  • #0 / RX - GPIO #0, also receive (input) pin for Serial1 (hardware UART). Also PWM out
  • #1 / TX - GPIO #1, also transmit (output) pin for Serial1. PWM out
  • SDA - the I2C (Wire) data pin. There's no pull up on this pin by default so when using with I2C, you may need a 2.2K-10K pullup. Also GPIO #21. Also PWM out
  • SCL - the I2C (Wire) clock pin. There's no pull up on this pin by default so when using with I2C, you may need a 2.2K-10K pullup. Also GPIO #22. Also PWM out
  • #4 - GPIO #4, PWM out
  • #5 - GPIO #5, PWM out
  • #6 - GPIO #6, PWM out
  • #9 - GPIO #9, PWM out
  • #10 - GPIO #10, PWM out
  • #11 - GPIO #11, PWM out
  • #12 - GPIO #12, PWM out
  • #13 - GPIO #13, PWM out and is connected to the red LED next to the USB jack
  • SCK/MOSI/MISO - These are the hardware SPI pins, you can use them as everyday GPIO #25/#24/#23 pins (but recommend keeping them free as they are best used for hardware SPI connections for high speed.)

Analog Pins:

  • A0 - This pin is analog input A0 but is also an analog output due to having a DAC (digital-to-analog converter). You can set the raw voltage to anything from 0 to 3.3V, unlike PWM outputs this is a true analog output
  • A1 - This pin is analog input  A1 but is also an analog output due to having a DAC (digital-to-analog converter). This is the second DAC, and is 'independent' of A0. You can set the raw voltage to anything from 0 to 3.3V, unlike PWM outputs this is a true analog output. Also can do PWM.
  • A2 thru A5 - These are each analog input as well as digital I/O pins. These pins can also do PWM.

I2S Pins:

  • #1/Tx - I2S bit_clock pin.
  • #10 - I2S word_select pin.
  • #11 - I2S data pin.

These pins are available in CircuitPython under the board module. Names that start with # are prefixed with D and other names are as is. So #0 / RX above is available as board.D0 and board.RX for example.

Parallel Capture Peripheral

There's a 'camera' input peripheral you can use with some camera chips to capture video with 8-bit data width. We thought this was neat so we made sure all those pins were available. Here are the PCC pins (left) and the Feather M4 pins it's mapped to. Unlike other peripherals, you cannot mux these signals to other pins!

  • DEN1: SDA
  • DEN2: SCL
  • CLK: D6
  • D0: D11
  • D1: D13
  • D2: D10
  • D3: D12
  • D4: MISO
  • D5: D5
  • D6: MOSI
  • D7: SCK

NeoPixel and LEDs

As part of the 'Express' series of boards, the Feather M4 CAN Express is designed for use with CircuitPython. To make that easy, we have added two extra parts to this Feather M4: a mini NeoPixel (addressable RGB LED) and a 2 MB QSPI (Quad SPI) Flash chip. There is also the little red LED, and a yellow charge LED.

NeoPixel LED - connected to pin #8 in Arduino, so just use our NeoPixel library and set it up as a single-LED strand on pin 8. In CircuitPython, the NeoPixel is board.NEOPIXEL and the library for it is here and in the bundle.

Unlike most other boards the NeoPixel is not powered by the 3.3V power supply - instead we power it from a separate GPIO pin. This lets us turn off the NeoPixel completely, removing the ~1mA quiescent current. To enable the NeoPixel, set the NEOPIXEL_POWER (CircuitPython) or PIN_NEOPIXEL_POWER (Arduino) to be an OUTPUT and HIGH. To disable it, set it to be an OUTPUT and LOW. (When used as a status LED, CircuitPython will automatically enable the power)

The NeoPixel is also used by the bootloader to let you know if the device has enumerated correctly (green) or USB failure (red). In CircuitPython, the LED is used to indicate the runtime status.

  • Red LED - connected to pin #13. It is user-controllable through code.
  • CHG LED - This LED is lit up when a battery is charging. If there is no battery attached, the yellow LED will flicker (it's looking for a battery!)

QSPI Flash

  • QSPI Flash - connected to 6 pins that are not brought out on the GPIO pads. This way you don't have to worry about the SPI flash colliding with other devices on the main SPI connection.

QSPI is neat because it allows you to have 4 data in/out lines instead of just SPI's single line in and single line out. This means that QSPI is at least 4 times faster. But in reality is at least 10x faster because you can clock the QSPI peripheral much faster than a plain SPI peripheral

However, the QSPI port is not also on an SERCOM. So, you have to either use the QSPI peripheral or bitbang SPI if you want to talk to the chip. We have an Arduino library here which provides QSPI interfacing for Arduino. In CircuitPython, the QSPI flash is used natively by the interpretter and is read-only to user code, instead the Flash just shows up as the writeable disk drive!

Other Pins

  • RST - this is the Reset pin, tie to ground to manually reset the ATSAMD51, as well as launch the bootloader manually
  • ARef - the analog reference pin. Normally the reference voltage is the same as the chip logic voltage (3.3V) but if you need an alternative analog reference, connect it to this pin and select the external AREF in your firmware. Can't go higher than 3.3V!
On the Feather M4 CAN Express, at least for now, AREF is tied to 3.3V due to a silicon v0 bug that does not allow the DACs to work unless AREF is connected to 3.3V. You cut the bottom jumper if you need a different AREF voltage but note that this may change DAC range!

Debugging Interface

If you'd like to do more advanced development, trace-debugging, or not use the bootloader, we have the SWD interface exposed. You'll have to solder to the two SWDIO/SWCLK pads on the bottom:

This guide was first published on Jan 25, 2021. It was last updated on Jan 25, 2021.

This page (Pinouts) was last updated on Sep 21, 2021.

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