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MT-D21E Microchip / Atmel SAMD21 / L21 / C21 ARM Cortex M0+ USB development board

Availability: In stock

Accepting MC, VISA, AMEX, Discover, PayPal

Quick Overview

Revision B now available!

● Choose the SAMD21, SAML21, or SAMC21.
● Optional SPI SRAM, EEPROM, or FLASH.
● Arduino support available at Github
● Arduino compatible USB CDC bootloader installed (D21 / L21).
● Two 20-pin 100-mil header sticks included.
● Optional Cortex debug / program header.

Rev B Manual

Please read below the options for configuration information.

   This item ships VAT free to most EU countries   
   if total is less than about $24.00 (€22.00).   

MT-D21E Rev B

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  • MT-D21E Rev B
  • MT-D21E Rev B pinout
  • MT-D21E Rev B bottom
  • MT-D21E Rev B schematic

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Configuration Options

Core Components:

Includes MCU (see below), 3.3V 250mA regulator (2uA quiescent), 32.768KHz crystal, 16MHz crystal, Blue LED, Reset button, Mini USB with ESD, 500mA PTC fuse, diodes, coin cell diode and capacitor, inductor for the L21 buck converter, voltage divider for Vin or Vbus, jumper, decoupling / filter capacitors, ferrite bead, and I2C / RST pullups.

Choose SAMD21, SAML21, or SAMC21 (256KB variants, see manual for more info):

D21E-256General purpose SAM M0+ MCU, USB, I2S, also used in the Arduino Zero.
L21E-256Low power features, enhanced analog peripherals, USB, crypto/TRNG, custom logic. Inductor installed (in place of 0ohm resistor) to support on-chip buck converter, no pin A28.
C21E-2565V support on board, MPU, 2x CAN instead of USB, Sigma-Delta and 2x SAR ADCs. Optionally connect Vcc to 5V. DO NOT install FLASH if using 5V.
CUSTOMSend email with choice of compatible MCU (ie: different FLASH capacity variant). It will usually ship within 1 week.

Choose Optional SPI Memory Device (all powered by Vcc and connect to MCU using SPI at up to 12MHz):

128KB SRAMCan connect Vbat header pin (coin cell) to SRAM backup pin. Consumes 4uA quiescent current.
1MB FLASHWith protection and OTP page. 2uA quiescent current. Do not use with >3.6V.
64KB EEPROMWith OTP page. Consumes 2uA quiescent current.

Choose Optional Cortex Header:

Cortex Header Not Included (CHN)
Cortex Header Installed (CHI)

All come with SAM-BA bootloader preinstalled:

USB CDC Serial supported with D21, L21, and D51
TTL Serial supported with C21

Revision B Changes:

*    Add support for more MCU options (SAMD, SAML, or SAMC)
      - With SAML, an inductor is installed to support the buck converter
      - USB Vbus can be connected to Vcc to support SAMC at 5V
*    Serial memory device can be installed
      (128K SRAM, 512KB FLASH, or 64KB EEPROM)
      - Using SPI at up to 12MHz using pins A18, A19, A22 (A27 for CS)
*    Added Vbat and Gnd pins (coin cell), can connect to SRAM,
      and/or Vcc (advanced)
*    Button A now jumper A to make room for memory device,
      used as CS for memory as well
*    Moved the blue LED to pin A6 (arduino pin 6),
      changed resistor to 1Kohm (600uA @ 3.3V)
*    Physically larger PTC fuse (0805) with
      higher trip (500mA) and hold (250mA)
*    Changed ESD device to protect Vbus in addition to D+ and D-


The MT-D21E is a development board for the 32-pin Microchip / Atmel SAMx21E ARM Cortex M0+ microcontrollers. Choose between the D21E (general purpose M0+ MCU, USB, I2S, also used in the Arduino Zero), L21E (low power features, enhanced analog, USB, crypto/TRNG, custom logic), or C21E (5V support, MPU, 2x CAN instead of USB, Sigma-Delta and 2x SAR ADCs). An optional SPI serial memory device can be mounted (128KB SRAM w/backup, 512KB FLASH, or 64KB EEPROM). The board can be powered from USB or the Vin pin, with 2 schottky diodes providing simple switching and reverse-polarity protection. This voltage is regulated to 3.3V by the onboard 250mA, extremely low quiescent current (2uA) LDO regulator which supports up to 16V on Vin. The C21 supports 5V operation by connecting USB Vbus to Vcc (jumpers). A 250mA (hold) PTC resettable fuse provides overcurrent protection. Also mounted is a mini USB connector with ESD protection, blue LED, 16MHz crystal, 32.768KHz crystal, button, jumper, and Vbat input. Arduino 1.6.x compatible core files (1.6.x, 1.8.x IDE) for all 3 chips are provided. A SAM-BA USB CDC bootloader (TTL serial only for C21) is preinstalled for programming without an external tool (Arduino or standalone use). The optional Cortex header (10-pin, 50-mil) can be used with an external debugger/programmer. There are 40 dual inline header pins with 0.1” pin spacing and 0.7” row spacing which allows for breadboard or perfboard mounting. The PCB measures 2.1” x 0.9” x 0.062” (52mm x 23mm x 1.6mm) with two 3mm mounting holes.


*    Microchip / Atmel ARM Cortex M0+ 32-pin microcontroller
            Choice of SAMD, SAML, or SAMC chips
                  D21E (general purpose SAM M0+ MCU, USB, I2S, also used in the Arduino Zero)
                  L21E (low power features, enhanced analog, USB, crypto/TRNG, custom logic)
                  C21E (5V support, MPU, 2x CAN instead of USB, Sigma-Delta and 2x SAR ADCs)
            CPU operates at up to 48MHz
            All chips available with up to 256KB FLASH and 32KB of SRAM
            All chips feature 6 timers, RTC, 4 SERCOM, DMA, PTC, AC
*   Optional SPI Serial Memory Device
           128KB SRAM with battery backup (Vbat pin)
           512KB FLASH with protection features and OTP page
           64KB EEPROM with OTP page
*   Onboard 3.3V, 250mA LDO regulator
           Supports up to 16V DC input on Vin pin
           Extremely low quiescent current (2.0uA typical)
           Over-current and over-temperature protection
*   Powered by USB Vbus or external power source on Vin (up to 16V)
           Simple diode power source switching,reverse-polarity protection
           With the C21E installed, USB Vbus can be connected to Vcc for 5V operation
*   Arduino 1.6.x compatible core (1.6.x, 1.8.x IDE)
*   SAM-BA USB CDC bootloader (D21 and L21 only, C21 has serial bootloader)
           Arduino compatible (use the Arduino IDE to upload)
           Bossa command line utility (Windows, Linux, limited OS X)
*   PTC resettable fuse (250mA hold / 500mA trip)
*   Optional Cortex Debug Header (10-pin, 50-mil) for device programming and debugging
*   16MHz crystal (use PLL for up to 48MHz cpu clock)
*   32.768KHz crystal (use PLL or FLL for up to 48MHz cpu clock)
*   Blue Status LED (can be disconnected)
*   Jumper A for general use (pin A27)
*   Button B configurable for reset or general use (pin A31) with debouncing
*   Two 4.7Kohm resistors can be connected to pins A16 and A17 for use with I2C
*   Mini USB connector with ESD protection on USB Vbus, D+, and D- lines
*   USB pins (or CAN on the C21) routed to header pins (for panel-mount connector)
*   Ferrite bead and 2 capacitors on analog supply
*   Two capacitors each can be enabled for pins A3 and/or A4 for use with external references
*   24 solder jumpers on PCB bottom for configuration flexibility
*   All PORT pins available on headers
*   2 main headers are on 0.1” spacing (breadboard/perfboard mounting), 0.7” apart
*   Two 3mm mounting holes (~5mm pad)
*   High-quality PCB with gold-plated finish
*   Measures approx. 2.1” x 0.9” (52mm x 23mm) and 0.062” (1.6mm) thick

Schematic for Rev B

CNC Drill File for Rev B


Arduino Support


Arduino support (1.6.x, 1.8.x IDE) is now available.

Drivers for Arduino and SAM-BA Bootloader


Signed drivers for the SAM-BA CDC bootloader and for Arduino (CDC, HID, MIDI, MSD).
See https://www.mattairtech.com/support/ for installation instructions.

SAM-BA Bootloader


These are the SAM-BA bootloaders that comes pre-installed.

SAM-BA Bootloader Utility

        These are the SAM-BA bootloader utilities for transferring firmware. D51 support coming soon.

bossac-1.7.0-mattairtech-2-mingw32-64.zip (Windows 32 bit and 64 bit)
Bossa-1.7.0-mattairtech-2-x86_64-linux-gnu.tar.gz (Linux 64 bit, includes Bossa GUI and Bossa shell)
bossac-1.7.0-mattairtech-2-i686-linux-gnu.tar.gz (Linux 32 bit)
bossac-1.7.0-mattairtech-2-x86_64-apple-darwin.tar.gz (OS X 10.5+, 64 bit) 

Test Firmware (Arduino blink sketch)


The Rev B blink sketch will be posted here soon.
The link is for the Rev A Arduino blink sketch with USB (CDC + HID). This comes optionally pre-installed.
See https://www.mattairtech.com/support/ for details.

MSD Bootloader Source and Binaries (Rev A only)


Blink Demo (MSD Bootloader or No Bootloader options) (Rev A only)


MT-D21E_Blink.zip contains the blink demo hex file that comes pre-installed (Rev A only).
It simply blinks the LED at 1Hz using an internal clock source.


This development board/kit is intended for use for FURTHER ENGINEERING, DEVELOPMENT, DEMONSTRATION, OR EVALUATION PURPOSES ONLY. It is not a finished product, and may not (yet) comply with some or any technical or legal requirements that are applicable to finished products, including, without limitation, directives regarding electromagnetic compatibility, recycling (WEEE), FCC, CE, or UL (except as may be otherwise noted on the board/kit). MattairTech LLC supplied this board/kit AS IS, without any warranties, with all faults, at the buyer's and further users' sole risk. The user assumes all responsibility and liability for proper and safe handling of the goods. Further, the user indemnifies Atmel from all claims arising from the handling or use of the goods. Due to the open construction of the product, it is the user's responsibility to take any and all appropriate precautions with regard to electrostatic discharge and any other technical or legal concerns.

The authors disclaim all warranties with regard to this software, including all implied warranties of merchantability and fitness. In no event shall any author be liable for any special, indirect or consequential damages or any damages whatsoever resulting from loss of use, data or profits, whether in an action of contract, negligence or other tortious action, arising out of or in connection with the use or performance of this software.

Accepting MC, VISA, AMEX, Discover, PayPal