nRF5340 multiple high-speed SPI slaves

[skruffen]

Hi,

When using HSPI pins on the nrf5340, it has a dedicated chip select pin HSPI_CSN. Does this mean that only one slave can be connected to the high-speed SPI?

Or, can I connect additional slaves and just use regular GPIOs for chip select?

[Simonr]

Hi

I heard back from the developers today, an here are their thoughts:

Since CSN is considered a "slow" signal in the sense of an SPI transfer, the use of a regular GPIO with software control is possible. The HW CSN offers tighter timing control (typically selecting slaves closer to the actual transaction). Another option to change between SPI slaves would be to disable the SPIM, change PSEL.CSN to the new slave and re-enable the SPIM. 

The limitation for using several SPI slaves with high-speed SPI is not so much the CSN but rather the load on the SCK, MISO and MOSI pins. Each additional SPI slave with its PCB routing will add capacitive load and affect the waveforms.

Best regards,

Simon

[skruffen]

Thank you for the help.

I have a better understanding now.