Connection of nRF21540 via SPI interface only

RE: Connection of nRF21540 via SPI interface only

backstreet.devisor — Fri, 30 Sep 2022 13:12:06 GMT

Thank you very much, Bendik!

You helped me a lot.

RE: Connection of nRF21540 via SPI interface only

Bendik Heiskel — Fri, 30 Sep 2022 12:57:03 GMT

Due to errata 13, all the input pins need to be pulled low during power down state. But the CSN pin needs to be high when not in power down, in order to not need a MCU GPIO pin for the CSN pin it can be tied together with the PDN pin.

The MISO, MOSI and SCK pins can be grounded when not using SPI.

RE: Connection of nRF21540 via SPI interface only

backstreet.devisor — Fri, 30 Sep 2022 12:18:23 GMT

Great. Thanks for the help.
Do the SPI pins have to be grounded?

RE: Connection of nRF21540 via SPI interface only

Bendik Heiskel — Fri, 30 Sep 2022 12:13:43 GMT

Using only GPIO is possible and supported in the nRF Connect SDK.

With only the GPIO interface only 2 different TX gain settings can be used, by default these are 10 and 20 dB.

https://infocenter.nordicsemi.com/topic/ps_nrf21540/chapters/device_control/doc/tx_power_control.html?cp=7_0_0_4_3

If only one antenna is used the ANT_SEL pin does not have to connected to the MCU, and can be grounded directly, this will default to always use the ANT1 pin. This brings the minimum number of MCU pins needed down to 4, MODE, RX_EN, TX_EN and PDN.

RE: Connection of nRF21540 via SPI interface only

backstreet.devisor — Fri, 30 Sep 2022 11:05:27 GMT

Thanks for the answer!
What if you do the opposite, connect only the MODE, RX_EN, ANT_SEL, TX_EN, PDN pins to the microcontroller, and leave the SPI pins unconnected? Is it possible to do it this way? I need to connect the nRF21540 to the microcontroller with as few pins as possible, but the software implementation should not be too complicated.

RE: Connection of nRF21540 via SPI interface only

Bendik Heiskel — Fri, 30 Sep 2022 08:37:25 GMT

Hi,

The nRF21540 can almost be fully controlled with only the SPI interface. The PDN pin is needed to control the power down, this can't be controlled using the SPI interface. MODE, RX_EN, TX_EN and ANT_SEL must all be connected to ground when not used.

Our SDKs does not have support for controlling the nRF21540 using SPI only, so you would have to implement this feature yourself.

Best regards,

Bendik