I've built a custom "teensy" board that uses the MKL04 chip. Problem is that only 1/3 of 20 boards are working (ie programming with Paul's bootloader code and then showing up as a USB device) - even after a super careful inspection for solder/placement problems under a microscope.
One possibility is that my crystal layout is marginal. When does the crystal get activated - by the code that the MKL04 pushes or not until later when code is (optionally) pushed from the PC? If the latter, I can rule out crystal problems.
Another thoughts on alternatives or how to pin down the problem? "lsusb" on the PC shows no USB device. The MK20 has voltage applied and the internal regulator is producing 3.3V. The USB lines are providing USB connector to MK20 connectivity.
Voltage to MK20, USB connection, MKL04 connection - seems simple. What else is needed to appear as a USB device after pressing the "program" button?
I haven't put an oscilloscope on it yet - not sure what to look for.
One possibility is that my crystal layout is marginal. When does the crystal get activated - by the code that the MKL04 pushes or not until later when code is (optionally) pushed from the PC? If the latter, I can rule out crystal problems.
Another thoughts on alternatives or how to pin down the problem? "lsusb" on the PC shows no USB device. The MK20 has voltage applied and the internal regulator is producing 3.3V. The USB lines are providing USB connector to MK20 connectivity.
Voltage to MK20, USB connection, MKL04 connection - seems simple. What else is needed to appear as a USB device after pressing the "program" button?
I haven't put an oscilloscope on it yet - not sure what to look for.