Timer in low power counter mode outputs 0 when input signal greater than 4MHz

[gat]

Hi,

In an application with a nrf52840, we measure the frequency by counting rising edge with PPI linking GPIOTE EVENTS IN and TIMER TASK COUNT

GPIOTE.EVENTS_IN -> PPI -> TIMER.TASK_COUNT

Every 10 ms we capture the timer task count value and clear the count.

We have two signals one (T) is around 5.5MHz and another one (A) is around 3.75MHz

The A signal works fine but I only get zeros with the T signal

So I tried to connect an input of the nrf52840 with the output of a LFG configured to output a square signal and I tested frequency from 3MHz to 5MHz.

Around 4MHz, the timer stopped working and only outputs zeros in the capture register.

Is there any know issue related or workaround ?

Best Regards,

Gabriel

[Turbo J]

Most of the peripherials in NRF52x run on the 16MHz clock, and you probably need to divide by 4 for the GPIOTE edge detector.

Not documented in the PS, though.

[Jørgen Holmefjord]

Hi,

See this post. As correctly stated by Turbo J, the maximum theoretical frequency is 4MHz.

Best regards,
Jørgen