NRF52832 External LF clock

RE: NRF52832 External LF clock

KPK — Wed, 21 Feb 2018 15:41:17 GMT

The problem was in the host processor side. The clock output was not enabled in the host and so the LFCLK could not start in the nRF52832.

It works once the host clock output was enabled.

RE: NRF52832 External LF clock

KPK — Tue, 20 Feb 2018 16:05:34 GMT

Sorry. I got confused between Softdevice and SDK. But here are the discussions that I was referring to, where using an external clock was said to be supported.

This Question and This question.

In the first, a softdevice was setup with this configuration. Am I missing something?

Or is that method only for when I do not use a Softdevice?

RE: NRF52832 External LF clock

Sigurd — Tue, 20 Feb 2018 15:54:05 GMT

I don't think it have been supported before. When the SoftDevice is enabled the BYPASS and EXTERNAL bit is set to 0 by the SoftDevice, and this cannot be changed after the SoftDevice is enabled. We might add support for this in the api in a future SoftDevice version.

EDIT: BYPASS and EXTERNAL bit is set to 0 only if the LFCLK is not already running before enabling the SoftDevice. I.e. workaround is to configure and enable LFCLK before the SoftDevice is enabled.

RE: NRF52832 External LF clock

Turbo J — Tue, 20 Feb 2018 15:44:11 GMT

Grounding the XL2 output was probably not a good idea - I would simply have left it open. This signal might be the one that is used internally for the clock output, too.

Try looking at the XL2 output with a scope when it is not shorted to ground.

RE: NRF52832 External LF clock

KPK — Tue, 20 Feb 2018 14:47:03 GMT

Hi,

That is unfortunate. From the previous answers in the forum, I understood that it was previously possible to do it. Is it somehow not supported in the recent Softdevices? In that case, would it help if I used an older Softdevice?

RE: NRF52832 External LF clock

Sigurd — Tue, 20 Feb 2018 14:42:38 GMT

Hi,

Unfortunately the current softdevice API does not support external LFCLK. I would recommend either to add a 32.768 kHz crystal oscillator to the design, or use the internal 32.768 kHz RC oscillator.