SPI manually select CS pin

RE: SPI manually select CS pin

bjorn-spockeli — Tue, 23 Oct 2018 09:30:25 GMT

Yes, if you want to control it your self with the GPIO HAL then you can initialize the SPI driver with .ss_pin = NRF_SPIS_PIN_NOT_CONNECTED.

RE: SPI manually select CS pin

TEJASWINI J — Mon, 22 Oct 2018 10:17:38 GMT

Hi Robert and Roger Clark!

We can disconnect a PIN during the SPI Bus Initialization itself right? ( .ss_pin = NULL)

or is it necessary to have not connected?

Please correct me if I am wrong.

RE: SPI manually select CS pin

Roger Clark — Fri, 16 Jun 2017 10:49:55 GMT

Generally just enabling the CS pin all the time can cause problems

Often the protocol for peripherals involves sending 1 or 2 byes with a register address, followed by writing or reading multiple bytes

However, devices often rely on CS going low to indicate that a new transfer is about to take place and that the next data from the MCU is a command e.g. READ REGISTER

You should check the data sheet for the peripheral you are using, to make absolutely sure it allows CS to be enabled all the time

(Personally I would not do this, because if you get out of sync you will be sending or receiving garbage , to or from the peripheral

RE: SPI manually select CS pin

djqtsg — Fri, 16 Jun 2017 09:33:57 GMT

Can I just use GPIO function to set or clear the CS pin ONCE in the beginning since I have only one SPI slave device connected my MCU?

RE: SPI manually select CS pin

Robert — Thu, 08 Dec 2016 10:34:06 GMT

Thank you Roger !

RE: SPI manually select CS pin

Roger Clark — Tue, 15 Nov 2016 22:39:40 GMT

You can define the SS pin as not connected

NRF_SPIS_PIN_NOT_CONNECTED

See

infocenter.nordicsemi.com/index.jsp

Then use GPIO in you code to assert the CS pin youself before calling the nrf_drv_spi_transfer and clear it in the completion callback etc.