5 years, 3 months ago.

UART remove pull up


What configuration are the UART pins put in, are they in pull up mode? I have a device connected hat has a 1K series resistor, when I look at the UART on a scope trace the voltage levels only go from 1.6 to 3.3v.

Would it be possible to alter it to pull to ground? If so how.

Many Thanks,

Hi Joe,

What target do you use?

posted by Desmond Chen 26 Dec 2018

1 Answer

5 years, 3 months ago.

Hi Joe,

Please refer to this file


In serial_init(), rx/tx pins are set in PullUp mode, you can set them to PullNone for your device setup.


- Desmond, team Mbed

Accepted Answer

You can't 'PullDown' on the KL25z:


Only PullUp or PullNone, so you will need an external resistor on that pin if you want to PullDown. Perhaps PullNone will be sufficient to work in this case.

posted by Paul Staron 28 Dec 2018