Pin Recommended usage

[jhc]

Hi all

In nRF52840_PS Pin assignments sheet, some pins Recommended usage is "Standard drive, low frequency I/O only", does that mean only low frequency (up to 10kHz) signal can be input or output on these pins?

for instance, UART with baudrate 115200 should not be assigned to these low-frequency IO?

[jhc]

Attach relevant screenshots:

[Vidar Berg]

Hello,

The recommendation is given to avoid or reduce potential interference of the RADIO.

for instance, UART with baudrate 115200 should not be assigned to these low-frequency IO?

Yes, you should not select any of the low-frequency IOs if the UART is going to be used while the RADIO is operating. Doing so may result in increased radio packet loss.

Best regards,

Vidar

[Poplar]

Hi Vidar

could you please show us in detail? for example, we assigned the pins to emulate SPI function, the frequency is about 10MHz, even we need to consider the harmonics, from 10Mhz to 2.4Ghz is so far, how could the RF performance be degraded by this?

and, if we do so, how worse would it be compared without doing that?

thanks.

[jhc]

Hello, thanks for your reply.

Do you have relevant test reports or documents for our reference?

We want to know how high the packet loss rate is caused by the interference generated by erroneously using LOW-FREAUQCY IO as HIGH-FREQUENCE.

[ketiljo]

The impact on the receiver will vary depending on the position of the pin, frequency of the signal and the current that's being sinked or sourced. 10 kHz is a fairly conservative number that ensures that the receiver isn't affected by a switching GPIO. At frequencies higher than 10 kHz, some packet loss may be observed and the impact will increase with the frequency.

Packet loss is caused by power supply noise, not in-band RF noise. 

At 10 MHz, the receiver performance will be severely degraded, especially for the pins near the radio (ANT pin)

[Poplar]

Hi Ketijo

thanks for the reply. does the power supply noise occur inside of the chip? is there any way to fix that by peripheral components?