nRF52 clock in and out

[Greg Nelson]

I have two related questions about nRF52 (nrf52832) which I have not been able to pinpoint from the documentation.

1. Can the 32MHz crystal connection be replaced by a 32MHz input if there is an existing clock in the system that meets the precision, tolerance, etc? On many processors, one of the two crystal pins may be used as an input while the other is left open if there is a driven external source, but I see no information about this for nRF52.

2. What is the most power-efficient way to get a high frequency clock output from the nRF52? Other ARM processors seem to offer direct "HFCLK" outputs to pins, but I can't find any related features in the nRF52 documentation. The best I've been able to guess is that the SPIM or PWM blocks could be used to provide a clock (8MHz or 16MHz respectively?) but each of those draws additional power and we don't (in this case) need the remaining functionality of the peripherals.

Thank you.

[Greg Nelson]

Just to be clear, for my second point, it is fine that I can't get 32MHz or 64MHz out ("the high frequency clock"); the design simply requires some clock in the MHz range ("a high frequency clock") and the power drawn by the nRF52 is orders of magnitude lower than typical crystal oscillators drawing several mA. We just want to get the power as low as possible.