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Arduino M0: ATSAMD21G18 ARM Cortex-M0 Board, 3.3V, USB US$30.36

Arduino M0: ATSAMD21G18 ARM Cortex-M0 Board, 3.3V, USB

With the Arduino M0, you will have the potential to create your most imaginative and new ideas for IoT devices, wearable technologies, high-tech automation, wild robotics and other not-yet-imagined adventures in the world of makers.

The Arduino M0 represents a simple yet powerful 32-bit extension of the Arduino Uno platform. The board is powered by Atmel's SAMD21 MCU, featuring a 32-bit ARM Cortex M0 core. The power of this core gives the board an upgraded flexibility and boosts the scope of projects one can think of and make. Moreover, it makes the M0 an ideal educational tool for learning about 32-bit application development.

The main difference between this board and the M0 Pro is that this board does not have the Atmel Embedded Debugger (EDBG) chip.

Arduino M0 Features

Operating Voltage3.3V
Input Voltage6V to 15V recommended
Input Tolerance4.5V to 20V
Digital I/O Pins20, w/ 12 PWM & UART
Analog Input Pins6, 12-bit ADC channels
Analog Output Pins1, 10-bit DAC
DC Current per I/O Pin7 mA
Flash Memory256 KB
Clock Speed48 MHz
Dimensions2.7 2.1 inches (PCB only; connectors extend)

Powering the Board

The Arduino M0 can be powered via a micro-USB connection or with an external power supply. The power source is selected automatically.

External (non-USB) power can come either from an AC-to-DC adapter (wall-wart) or a battery. The adapter can be connected to the board by plugging a 2.1mm center-positive plug into the board's power jack. Leads from a battery can be inserted into the Gnd and Vin pin headers of the POWER connector. External power is required when the 500mA provided via USB is not enough to power a connected USB device is a USB Host application.

If you have both external and USB power sources connected, the board will give priority to the external source, switching automatically to USB if the external source is removed.

The power pins are as follows:

  • VIN The input voltage to the Arduino board when using an external source. You can supply voltage through this pin, or, if supplying voltage via the power jack, access it through this pin. The allowed input range is 6-20V.
  • 5V The regulated power supply used to power the microcontroller and other components on the board. This can come either from VIN via an on-board regulator, or be supplied by USB or another regulated 5V supply. The maximum current output provided by the on-board regulator is 1A (according to the power input source).
  • 3V3 A 3.3-volt supply generated by the on-board regulator. Maximum current draw is 1A according to the power input source.
  • GND Ground pins.
  • IOREF The voltage at which the I/O pins of the board are operating (i.e. VCC for the board). This is 3.3V on the M0.


The ATSAMD21G18 has 256KB of Flash program memory (with 4KB used for the bootloader). The bootloader is factory pre-burnt by Atmel and is stored in dedicated ROM. The bootloader is protected using the NVM fuse. The board also has 32KB of SRAM and up to 16KB by emulation of EEPROM, which can be read and written using the EEPROM Library.

Input and Output

Each of the 14 digital I/O pins on the M0 can be used as an input or an output, using pinMode(), digitalWrite(), and digitalRead() functions. They operate at 3.3V. Each pin can provide or receive a maximum of 7mA and has an internal pull-up resistor (disconnected by default) of 20-60 kOhms. In addition, some pins have specialized functions:
  • Serial: 0 (RX) and 1 (TX) Used to receive (RX) and transmit (TX) TTL serial data using the ATSAMD21G18 hardware serial capability. Note that on the M0, the Serial class refers to USB (CDC) communication; for 3.3V serial on pins 0 and 1, use the Serial1 class.
  • TWI: SDA and SCL Support TWI communication using the Wire Library.
  • PWM
  • Pins 2 through 13 provide 8-bit PWM output with the analogWrite() function. The resolution of the PWM can be changed with the analogWriteResolution() function. Note: Pins 4 and 10 can not be used simultaneously as PWM; neither can pins 5 and 12.
  • SPI (on the ICSP header) These pins support SPI communication using the SPI Library. Note that the SPI pins are not connected to any of the digital I/O pins as they are on the Uno. On the M0, they are available only on the ICSP connector. This means that if you have a shield that uses SPI but does not have a 6-pin ICSP connector that connects to the M0's 6-pin ICSP header, that shield will not work.
  • LED: 13 There is a built-in LED connected to digital pin 13. When the pin is High value, the LED is on; when the pin is Low, it's off.
  • Analog Inputs: A0 - A5 The M0 has six analog inputs, labeled A0 through A5. Pins A0-A5 appear in the same locations as on the Uno. Each analog input provides 12 bits of resolution (i.e. 4096 different values). By default, the analog inputs measure from ground to 3.3V, though is it possible to change the upper end of their range using the AREF pin and the analogReference() function.
  • DAC Pin A0 provides true analog output with 10-bit resolution (1023 levels) with the analogWrite() function. This pin can be used to create an audio output using the Audio Library.
  • Reset Bring this line Low to reset the microcontroller. This is typically used to add a reset button when shields are used that block the one already present on the board.


The M0 has a number of facilities for communicating with a computer, another Arduino, or other microcontrollers, and with different devices like phones, tablets, cameras and so on. The SAMD21 provides one hardware UART and three hardware USARTs for 3.3V serial communication.

The Arduino software includes a serial monitor which allows simple text data to be sent to and from the board. The RX and TX LEDs on the board will flash when data are being transmitted via the ATSAMD21G18 chip and USB connection to the computer (but not for serial communication on pins 0 and 1).

The Native USB port is connected to the SAMD21. It allows for serial (CDC) communication over USB. This provides a serial connection to the Serial Monitor or other applications on your computer.

The SAMD21 also supports I2C (TWI) and SPI communication. The Arduino software includes a Wire Library to simplify use of the TWI bus. For SPI communication, use the SPI Library.


The M0 can be programmed with the Arduino software. Note that if you're using a Linux-based OS, be sure to follow the Guide to using Arduino in Linux.

Uploading sketches to the SAMD21 is different from how it works with the AVR microcontrollers found in other Arduino boards: the Flash memory needs to be erased before being re-programmed. Upload operation is managed by a dedicated ROM area on the SAMD21.

The USB port can be used to program the board. Select Arduino M0 (Native USB Port) as your board in the Arduino IDE. The Native USB port is connected directly to the SAMD21. Connect the M0 Native USB port to your computer. Opening and closing the Native port at 1200bps triggers a "soft erase" procedure: the Flash memory is erased and the board is restarted with the bootloader. Opening and closing the native port at a different baudrate will not reset the SAMD21.

USB Overcurrent Protection

The M0 has a resettable polyfuse that protects your computer's USB ports from shorts and overcurrent. Although most computers provide their own internal protection, the fuse provides an extra layer of protection. If more than 500mA flows through the USB port, the fuse will automatically break the connection until the short or overload is removed.

Physical Characteristics

The maximum length and width of the M0 PCB are 2.7 and 2.1 inches respectively, with the USB and power connectors extending beyond. Four screw holes allow the board to be attached to a surface or case. Note that the distance between digital pins 7 and 8 is 160 mil (0.16") not an even multiple of the 100-mil spacing of the other pins. (This is a legacy arrangement from the original Arduino's design flaw, maintained for compatibility with Arduino Shields.)

Arduino M0 Resources

The various links above on this page can be found also from the the starting points listed below.

This product was added to our catalog on Thursday 28 January, 2016.


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