Custom Teensy without USB


New member
I would like to design a custom device based on the Teensy 4.1 schematic, but without a USB port. My plan is to use the MKL02 bootloader IC, to help with the power-up sequence etc. but expose an external JTAG connector that if connected would disable the connections to the MKL02 IC for TMS, TCK, TDI, TDO, and TRST via a bit bus switch(es) like the NXP 74CBTLV3125-Q100. Hopefully this would both allow me to upload my Teensy HEX file via JTAG as well as some hardware debugging. Has anyone done anything similar and can share some pointers, and does anyone know that if I take this approach, whether I need to do anything with any of the other MKL02 pins (e.g. do I need to connect MOD to ground to allow flashing)?