AnsweredAssumed Answered

MK20DX128VLF5 does not boot without an external 16Mhz xtal

Question asked by Chris Seto on Jun 19, 2019
Latest reply on Jun 20, 2019 by Mark Butcher



I have an MK20DX128VLF5 on my board. It is connected to an external single ended oscillator. This chip will seemingly not exit POR. In debugging, I was trying to determine the clock configuration on a fresh reset. It seems like the chip should boot from its internal osc and run off of that until switched to the external clock by user code. I have a known good board with the same chip and an xtal, so I pulled the xtal to see if the chip still booted without it. It did not. Jtag works on both chips, but it looks like the reset handler is never running. Additionally, it seems like the reset line is oscillating up and down. The resrt line is not connected to anything else outide of jtag, and this behavior persists if htag is disconnected. 


The K20 should be able to boot by itself without any external clock, correct?