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Minimal K20 breadboard prototype

Question asked by Roger Collins on Sep 21, 2013
Latest reply on Oct 4, 2013 by Roger Collins

My goal here is to just make a "hello world" prototype to test using internal voltage regulator, internal clock, JTAG interface, and a uart console.  I have not added any connections to the UART yet.  See pic below.  All the wires going off the left edge are not connected to anything - they are meant to be connected to the JTAG debugger (PEM Multilink Universal with standard ARM connector) but not yet.


Ignoring the disconnected JTAG wires, connections are


VREGIN -> +5V from 7805 voltage regulator with caps 100u on input, 1u on output

VDD (both) -> VOUT33 with .1u decoupling caps

VSS (both) -> ground

RESETb -> 10K pullup with a 1u cap (which I don't think I need) to VOUT33


This MCU is MK20DX128VL5.


Happy to report that VOUT33 looks stable. I had to add some of the caps above to cleanup the 5V to get that working.


My problem is that RESET never goes high.


What have I missed? Any ideas on why the RESET pin always measure ~0V, why MCU is not coming out of reset and releasing the RESET pin?