Reset held asserted at first power-up -- K20

garyk_ — Wed, 22 Jul 2015 17:24:25 GMT

I've designed a PCB that uses the MK20DX256VLH7. Upon first power-up, the microcontroller appears dead. No 16MHz XTAL oscillation, and the DX256's RESET pin is held asserted. Supply voltage is steady at +3.3V. AT this stage, I've not attached any other devices to the DX256, other than a USB connector.

What issues could be causing the part to be stalled like this? I'm very perplexed at this point.

Many thanks, in advance!

Re: Reset held asserted at first power-up -- K20

kerryzhou — Thu, 23 Jul 2015 02:38:17 GMT

Hi Gary Kitten,

Actually, to a new chip without program, your phenomena is normal.

16MHZ external oscillator is not oscillating, it is because you didn't enable the OSC in the chip with program.

To a new chip, if you add 4.7K to 10k pullup resistor in the RESET_b pin, and connect a 100nf capacitor to ground, the reset pin should have the oscillator wave, you can check it through the oscilloscope.

You can create a sample project, to check whether your chip can download program.

After the chip have programed, it will work normally.

Wish it helps you!

Have a great day,
Jingjing

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Kinetis MicrocontrollersのトピックReset held asserted at first power-up -- K20

Reset held asserted at first power-up -- K20

Re: Reset held asserted at first power-up -- K20