Programming an MK20DX256VLH7 (Teensy 3.2)

Teensy is an arduino compatible prototyping board that offers fast clock speeds and a ton of other features compared to the mainstream AVR based arduino boards. One of them is teensy 3.2, which has alot of support and libraries available.

Lets suppose you are working on a project and you need the MCU chip soldered onto your own PCB. The question is, how do you program/burn the firmware onto the MK20DX256VLH7 chip? Well, lets take a look at the teensy 3.2's schematic.

The MKL02Z32VFG4 chip contains the teensy bootloader (shown in red) which performs handshake with the PC and puts the firmware on the main MK20DX256VLH7 chip. Fortunately, the MKL02Z32VFG4 chip with teensy bootloader installed is sold on the teensy homepage. I got my hands on a few and made a PCB that replicates the schematic of teensy 3.2. And voila, it worked fine.

This meant that each PCB must contain an MKL02Z32VFG4 chip and the main teensy 3.2 MCU as well. I needed a few tens of these PCBs made and couldn't afford to put two MCU chips along with all the components on my PCB due to space constraints. So I came up with an idea to re-use the MKL02Z32VFG4 and program several MK20DX256VLH7 before soldering.

Looking at the teensy 3.2 schematic, the programming MCU has PTA0, PTA2, PTA3 and reset lines going to the MK20DX256VLH7. USB lines are directly connected to the MK20DX256VLH7.

Lets separate these two chips and make separate boards for programming purposes. Lets take a look at the schematic below.

The MKL02Z32VFG4 chip is the heart of this circuit. A mini USB connector connects it to the PC. A molex 503480-0800 connector connects to the other PCB that has the MK20DX256VLH7 chip(lets talk about that later). For now, we have separated the MKL02Z32VFG4 from the MK20DX256VLH7 and placed a connector to later carry the programming signals to the MK20DX256VLH7.

Now lets take a look at the other board's schematic.

This only has basic connection to the MK20DX256VLH7 and contains a QFP64 0.5mm socket. This board also needs 5V of external power. These two boards are connected using an 8-conductor FFC cable. The gerber images are as follows:

Tested the boards, worked like a charm. Here are some actual pics of the boards.

The Eagle schematic/board files are available on request.

Disclaimer. This work is not intended for commercial/sales purposes. Use for personal/educational purposes only.