nRF52832 2.048 MHz Clock

[Vala]

Hi,

I want to generate a 2.048MHz clock on one of the IOs of nRF52832. Could you comment on following questions?

1- Can I generate this frequency (with no load on CPU), using a 32MHz crystal or I have to use a more accurate crystal?

2- What is the most optimized way for doing so, from power consumption and clock accuracy point of view? A PWM or timer + compare + PPI?

-Vala

[Jørgen Holmefjord]

Hi,

You can generate a clock as described in this thread.

What kind of accuracy do you need?

Best regards,

Jørgen

[Vala]

Thanks for your reply. Yes I had seen this thread. Just wanted to ask about this specific frequency (2.048 MHz) with a 32MHz crystal. If my calculation is correct, there is no way to achieve this frequency with a 32 MHz crystal. For instance, if the peripheral clock is 16MHz, the timer prescaler is 1 and the compare value is 8, then the output will be 2MHz (assuming that the timer resets after reaching the compare value), which is not acceptable in my project.

Well, about the accuracy basically the highest that I can achieve, of course with a compromise acceptable by other limiting factors in the project. Power consumption and limited PCB area are the two that probably affect this issue. Due to the small board area, I don't want to add an extra crystal for the sensor (the one that requires this 2.048M). Therefore, I thought that changing the the crystal for nRF52832 can be one solution.

[Jørgen Holmefjord]

Yes, you could get 2 MHz, but not 2.048 MHz. If you are not using any of the radio features of the nRF52, you could use the internal oscillator, HFINT. The HFXO must be running to use the RADIO, NFC module or the calibration mechanism associated with the 32.768 kHz RC oscillator. If you use Bluetooth, a tolerance of ±40 ppm is required for HFXO (±60 ppm for proprietary 2.4 GHz). You can therefore not swap it for another crystal if you use the radio.

[Vala]

Thanks for your comment. This is the answer that I was looking for. I am using BLE. Therefore, the only option left is to use an external crystal for the sensor.