Why there are some pins cant be the ss pin of SPI

[Aku]

HI

I'm using SPI connecting to mutiple max31856(two now) on nrf52DK and SDK15.3

so I control my ss pin to pull low by myself 

chip select by changing spi_pin like some code below

void MAX31856_setThermocoupleType(max31856_thermocoupletype_t type ,uint32_t spi_pin)
{   
    nrf_gpio_pin_clear(spi_pin);
    MAX31856_write_reg(MAX31856_CR1_REG);
    uint8_t t = MAX31856_read_reg(0xFF);
    nrf_gpio_pin_set(spi_pin);

    t &= 0xF0; // mask off bottom 4 bits
    t |= (uint8_t)type & 0x0F;

    nrf_gpio_pin_clear(spi_pin);
    MAX31856_write_reg(MAX31856_CR1_REG|0x80);
    MAX31856_write_reg(t);
    nrf_gpio_pin_set(spi_pin);
}

my miso is 5, mosi is 7 , sck is 8

and ss1 is 6 , ss2 is 9 at first

then i found that ss1 works fine ,but ss2 doesnt

SO I TRY OTHER PINS, AND FOUND THAT pin 2,3,4,6,12,13,14,15,18,19,20,22,23,24,26,27,28,29,30,31 can work

BUT pin 9,10,11,13,17,21,25 cant work

MY QUESTION  is why that happened

thanks

[Nguyen Hoan Hoang]

Pin 9 is by default NFC.  To use it, you need to configure in the UICR register for that pin to act as GPIO.

    /* Configure NFCT pins as GPIOs if NFCT is not to be used in your code. If CONFIG_NFCT_PINS_AS_GPIOS is not defined,
       two GPIOs (see Product Specification to see which ones) will be reserved for NFC and will not be available as
       normal GPIOs. */
    #if defined (CONFIG_NFCT_PINS_AS_GPIOS)
        if ((NRF_UICR->NFCPINS & UICR_NFCPINS_PROTECT_Msk) == (UICR_NFCPINS_PROTECT_NFC << UICR_NFCPINS_PROTECT_Pos)){
            NRF_NVMC->CONFIG = NVMC_CONFIG_WEN_Wen << NVMC_CONFIG_WEN_Pos;
            while (NRF_NVMC->READY == NVMC_READY_READY_Busy){}
            NRF_UICR->NFCPINS &= ~UICR_NFCPINS_PROTECT_Msk;
            while (NRF_NVMC->READY == NVMC_READY_READY_Busy){}
            NRF_NVMC->CONFIG = NVMC_CONFIG_WEN_Ren << NVMC_CONFIG_WEN_Pos;
            while (NRF_NVMC->READY == NVMC_READY_READY_Busy){}
            NVIC_SystemReset();
        }
    #endif

[Aditya Jethva]

Can you share me the whole code , i  tried in NRF51822 but not getting the data .

[Simonr]

Hi

The nRF51822 does not support NFC, and therefore does not have NFC pins that need configuring. Please check out the SPI examples in SDK v12.3, which is the latest one supporting the nRF51 series devices. 

This case is specific to the nRF52's use of some GPIOs. If you're having trouble with setting up a project. Please create a ticket of your own where you describe your issue in detail.

Best regards,

Simon