Pin status under sleep & Pin usage

[Alex.Pan]

Hi : 

 we met some quesiton when using nRF52840: 

1.  Is it possible to drive a pin to high or low in sleep mode? For eg. we would like to put pin P0.12(may be other pins)to high during sleep(fully 256kRAM retaention), is it possible?

2.  For the Recommended usage of the nRF52840 pins, most of the pins are marked as "standard drive,low frequency I/O only". what does "low frequency I/O only" .As specified in the note, the max frequency of the low frequency I/O signal is 10kHz. Does it means that the max input/output frequency of the pins is only 10kHz? 

    But accordiing to Part “6.17  PWM-Pulse width modulation” , all the GPIO can be configured a PWM outpint through PSEL.OUT[n], and the maxoutput frequecy of the PWM can be higher than 10kHz.we have test the waveform of the pins at 50kHz, it's ok. 

   So i'm little confused by  "low frequency I/O only" . Will frequecny higher than 10kHz reduce the lifetime of the MCU or may damaged the MCU? 

3. What's the fucntion of the pin  P0.18/nRESET during MCU start up? Will low signal on P0.18/nRESET keep the MCU in reset mode during startup? or P0.18 is just a GPIO, low signal on     P0.18 will not keep the MCU in reset mode during start up and RESET function will available after configureing.

Thanks very much!

Best regards!

[ketiljo]

1. All pins will be retained in sleep mode. 

2. Low freqyency I/O means that the radio may be affected by the data activity on the pins, but only when the radio is active (TX or RX). At all other times, you can use it as you want.

3. This pin can be assigned to be a reset pin instead of P0.18. But it will not take the role as the reset pin until after the device is out of POR (power on reset).

[Alex.Pan]

Hi ketiljo:

  Thanks for your feedback!

So:

1.   If the input/output frequcny on Low freqyency I/O pins below 10kHz will not affect the radio function, right?

2.  How about Low freqyency I/O pins configured as SPI(UART etc) interface? Will they affect the radio function when the baudrate above 10kHz?

Thanks very much!

Best regards!

[ketiljo]

1. Correct, the frequencies below 10 kHz will not affect the radio.

2. If you need UART or SPI, you should use other pins. You may have reduced RX performance of the low freq I/O pins are used for this.