open drain output to GPIO input pin with pulluphttps://devzone.nordicsemi.com/f/nordic-q-a/27170/open-drain-output-to-gpio-input-pin-with-pullupHi I have a charger IC for a lithium ion battery on a custom board with an nRF52832. It&#39;s this one, from ST Micro, an STBC08: www.st.com/.../stbc08.html The charger IC has two outputs, one to indicate that it has power from the USB bus, and anotheren-USTelligent Community 13Mon, 13 Nov 2017 04:12:28 GMTRE: open drain output to GPIO input pin with pulluphttps://devzone.nordicsemi.com/thread/107033?ContentTypeID=1Mon, 13 Nov 2017 04:12:28 GMT137ad170-7792-4731-bb38-c0d22fbe4515:7f619292-e50a-47fe-91c3-dad51e1564b0Eliot Stock<p>This was because the pins I was using for GPIO inputs were also the NFC pins and I had not done everything explained in this post to configure them as no longer used by NFC:</p> <p><a href="https://devzone.nordicsemi.com/question/96013/how-to-enable-p009-and-p010-as-gpio-pins-on-the-nrf52-instead-of-nfc-pins/">devzone.nordicsemi.com/.../</a></p><div style="clear:both;"></div>RE: open drain output to GPIO input pin with pulluphttps://devzone.nordicsemi.com/thread/107032?ContentTypeID=1Thu, 12 Oct 2017 01:24:42 GMT137ad170-7792-4731-bb38-c0d22fbe4515:f7b28857-9b17-4bb9-bc91-dca2e61b71b5RK<p>why don&#39;t you measure the input resistance of the &#39;open drain&#39; pins and see what it actually is. Some are better than others. Your figures would indicate that it&#39;s only about 10k which seems rather low.</p><div style="clear:both;"></div>