MK20DX256
開機流程
參考資訊：
1. building-your-own-custom-teensy
Just to give you an idea how the Teensy actually works: As you can see the boot loader MCU (Mini54Tan) is not directly connected to USB. Only the MK20 is connected to the USB. When you power the Teensy the MK20 will either run the program previously programmed via the Teensy loader (which is triggered by the Arduino IDE) or will wait for the Teensy loader to send a program. Pressing the button on Teensy pulls the P5.2 on Mini54Tan low. That triggers the boot loader MCU which immediately programs the MK20 via SWD (Serial Wire Debug) with a small program that activates the USB part of the MK20 and implements the counterpart of the Teensy loader. After the MK20s USB is activated it will be discovered by your Mac, Windows or Linux PC. Teensy loader waits for this USB discovery and will then send it’s current program to the MK20.
P.S. Teensy 3.1/3.0是Mini54Tan，Teensy 3.2則是MKL02Z32VFG4