SPI slave not working on pins 26,27

[Ryan]

Hello,

First, my setup is as follows: nRF51822 Rev. 3 dev board (PCA10028) s110 7.1 SDK 6.1.0

I am developing firmware on the PCA10028. I am matching SPI to a custom board I have already built and have a SPI master tied to the following pins on the nRF: MOSI 21 MISO 24 CLK 26 CS 27

My firmware uses spi_slave.c and I cannot get SPI to respond when CLK or CS are set to pins 26 or 27. nRF51822_PS v3.1 specifies that pins 26 and 27 can function as General purpose I/O, ADC input, or crystal connection for 32768 kHz. Do I need to set the pin functionality somewhere? Is spi_slave not able to do this? I cannot find how to do this.

Thanks

[RK]

You're trying to use P0.26 and P0.27 on the PCA10028? The PCA10028 manual says this

"On the DK board, P0.26 and P0.27 are by default used for the 32.768 kHz crystal and are not available as a GPIO on the connectors."

If you don't want the crystal you can cut SB1/2 and solder SB3/4 to remove it and use the pins as GPIOs, if you're really out of GPIOs to use.

[Ryan]

Thank you for the response. That makes sense. On my custom board without a 32.768 kHz crystal should I have any issues using 26 and 27 for SPI or will I need to set something in the firmware?