nRF52840 DK set UART RX to P0.09

Question

Hi,

I am using https://github.com/NordicDeveloperAcademy/nRF-Connect-SDK-Fundamentals lesson5/fund_less5_exer1. I am able to receive UART message using default UART RX P0.08 pin. But, when I change the UART RX to P0.09 using this overlay code it does not work.

&uart0 {
    pinctrl-0 = <&uart0_default>;
    pinctrl-1 = <&uart0_sleep>;
    pinctrl-names = "default", "sleep";
};
   
&pinctrl {
    uart0_default: uart0_default {
        group1 {
            psels = <NRF_PSEL(UART_TX, 0, 10)>;
        };
        group2 {
            psels = <NRF_PSEL(UART_RX, 0, 9)>;
            bias-pull-up;
        };
    };
   
    uart0_sleep: uart0_sleep {
        group1 {
            psels = <NRF_PSEL(UART_TX, 0, 10)>;
        };
        group2 {
            psels = <NRF_PSEL(UART_RX, 0, 9)>;
            bias-pull-up;
        };
    };
};

I got this overlay code from this post. https://devzone.nordicsemi.com/f/nordic-q-a/93648/change-uart-port

Regards,

Markel

Håkon Alseth · Accepted Answer

Hi, 
 
 P0.09 / P0.10 are NFC pins, and require some adjustment if you want to use them as GPIOs on the nRF52840-DK: 
 https://infocenter.nordicsemi.com/topic/ug_nrf52840_dk/UG/dk/hw_nfc_if.html?cp=5_0_4_7_10 
 
 In addition, you need to specify in UICR that the nfct pins are to be used as gpios: 
 &uicr {
	nfct-pins-as-gpios;
};

An alternative option is to choose any other available GPIOs you have in your design. 
 
 Kind regards, 
 Håkon

nRF52840 DK set UART RX to P0.09

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