Unable to configure pins 8 & 9 as SCL and SDA on BMD300 (nrf52832)

[asifmahmood]

I am using pin 8 (NFC pin) as SCL and pin 9 as SDA of nrf52832 on my custom board. Basically I have connected MPU9250 with these pins and I know that MPU9250 is NRFND, for testing I guess its OK to use. I have used 4.7k resistor for pull-up. For firmware part I am using nrfx library. When I use this library to configure other pins it works but not for these pins. 

#include <zephyr/kernel.h>
#include <stdio.h>
#include "twi.h"
#include "mpu9250.h"

int main(void)
{
    int err;

    err = twi_init(8U, 9U);
    if (err != 0)
    {
        printk("\rcould not initialize i2c\n");
    }

    err = twi_enable();
    if (err != 0)
    {
        printk("\rcould not enable i2c\n");
    }

    uint8_t dummy[] = { 1, 2, 3, 4, 5 };
    if (err == 0)
    {
        while (true)
        {
            err = twi_write(0xAA, 0xBB, dummy, sizeof(dummy));
            if (err != 0)
            {
                printk("\rcould not enable i2c\n");
            }
        }
    }
    printk("Hello World! %s\n", CONFIG_BOARD);
    return 0;
}

[Kazi Afroza Sultana]

Hello,

Pin 9 (P0.09) is used for NFC1 antenna pin. You can try to set other pin as SDA and see the change?

Here is the pin assignment o nRF52832 https://infocenter.nordicsemi.com/topic/com.nordic.infocenter.nrf52832.ps.v1.1/pin.html?cp=5_2_0_3#pin_assign .

Thanks.

BR

Kazi

[asifmahmood]

As per infocenter.nrf52832 pin 9 can also be used as General purpose I/O by disabling NFC using UCIR. But how? Which function I can use for this and where?

[Kazi Afroza Sultana]

Hello,

Yes. It is possible to set the NFC pin as GPIO pin. It is possible to set NFCPINS register. 

Did you disconnect the R25 and R26 from NFC pin and short R27 and R28 with 0ohm Resistor to the pins?

There is an old case you can look at:

(+) nrf52 enabling gpio on nfc pins - Nordic Q&A - Nordic DevZone - Nordic DevZone (nordicsemi.com)

The content of the NFCPINS register is reloaded at every erase. So, sometimes the past programmed application may enable NFC, hence the NFC pins have been set in the UICR. You can try to execute ''nrfjprog --eraseall'' command from command line to erase the UICR.

[asifmahmood]

Adding preprocessor define worked. Thanks for the help.