Teensy 3.1

The PJRC Teensy 3.1 operates at CPU frequency of 96MHz. The powerful ARM-M4 Freescale MK20DX256VLH7 MCU has 256 kB of flash memory, 64 kB of RAM memory. This platform is used in conjunction with the Teensy Loader program to download the mbed generated .HEX program code.


With a 28 pin DIP, small footprint, powerful M4 core and 256k Flash, the Teensy3.1 is an ideal platform for MCU 'drop-in' applications that require larger program sizes and speed. The mounting pins are standard .1" (2.54mm) spacing which make it easy for bread boarding or mounting on a development PCB. Teensy3.1 mbed library utilizes the same pin definitions as the Freescale FRDM platforms making it simple to transport existing programs. Adding a 32KHz crystal and back up cell, the RTC is fully functional during power down states.

Using USBSerial from the mbed USBDevice library will enable connection to your PC terminal and other devices.

Top View


Bottom View



Processor MK20DX256VLH7

  • Core Cortex-M4
  • Rated Speed 96 MHz
  • System Bus Speed 48 MHz
  • Flash Speed 24 MHz
  • Flash Memory 256 Kbytes
  • RAM 64 Kbytes
  • EEPROM 2 Kbytes
  • Digital I/O (34 Pins)
  • Voltage Output 3.3v
  • Voltage Input 5v Tolerant
  • Analog Input (21Pins)
  • Converters (2)
  • Resolution (16 Bits)
  • Comparators (3)
  • Analog Output (1 Pin)
  • DAC Resolution (12 Bits)
  • Timers (12 Total)
  • USB (Host/Device)
  • Serial (3)
  • SPI (1)
  • I2C (2)
  • CAN Bus (1)
  • I2S Audio (1)
  • RTC (date/time) Requires a 32.768 kHz crystal & 3V battery connected to Vbat.

Instructions to use Teensy 3.1 on mbed. (Windows)

The mbed compiled output will be in .HEX format and will need the Teensy Loader program to transfer the file to the Teensy.

/media/uploads/star297/teensy_loader.png (Image shows a different board, but the process is the same)

Download the Teensy Loader from PJRC:


(Further details on how to install and use are also available there.)

Compile and save the .HEX output file to the desktop or any other preferred folder on your PC. The complied .HEX output will appear large, however the build details will show the correct Flash/Ram values. With the Teensy 3.1 connected to your PC, start the Teensy Loader program. Select 'File - Open HEX File' or click the Open HEX File icon. This will bring up the 'Open File' dialog box. Select the mbed output .HEX file you just saved. Press the 'Bootloader Mode Button' on the Teensy 3.1 The Teensy Loader icons will change from greyed out to active. Select 'Operation - Program' or click the program icon. The file will transfer (quickly) to the Teensy 3.1

To run your downloaded program, either click the 'Reboot' icon or power cycle the Teensy 3.1

Important: The switch button on the Teensy 3.1 is for program download mode only, it will not reset and/or start your program. If you press it at any time the Teensy 3.1 will go into program mode and remain there until the board is power cycled or the 'Reboot' is selected on the Teensy Loader (if connected to your PC). For external hardware reset, a connection will need to be made to the pad marked 'R' on the underside of the board.



Further Information

For further detailed hardware information, see the Teensy 3.1 page at PJRC:



mbed will only support original PJRC Teensy 3.1 boards, counterfeit or clones will not work. All questions regarding the use of Teensy 3.1 on mbed must be directed to the Community Contributors or the mbed forum.

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