nRF54LM20B UART Communication

[VinayKotadamakki]

Hi Team,

Currently I am working with nRF54LM20 DK. And tried to import and use echo bot example from SDK. 
And modified the overlay file as per the UART pin changes required for my application. But I am not able to see any UART prints on console.
Adding overlay file contents here

&pinctrl {

    uart21_default: uart21_default {
        group1 {
            psels = <
                NRF_PSEL(UART_TX, 1, 2)   /* TX → P1.02 */
                NRF_PSEL(UART_RX, 1, 3)   /* RX → P1.03 */
            >;
        };
    };

    uart21_sleep: uart21_sleep {
        group1 {
            psels = <
                NRF_PSEL(UART_TX, 1, 2)
                NRF_PSEL(UART_RX, 1, 3)
            >;
            low-power-enable;
        };
    };
};

&uart21 {
    status = "okay";
    current-speed = <115200>;

    pinctrl-0 = <&uart21_default>;
    pinctrl-1 = <&uart21_sleep>;
    pinctrl-names = "default", "sleep";
};


/ {
    chosen {
        zephyr,console = &uart21;
    };
};

Please let me know the issue I am facing to use this bus.

Thanks and regards,

Vinay

[Vidar Berg]

Hi,

Do you have an external UART-USB bridge connected to these pins to bridge the serial communication to your PC? If not, you need to use the default pin assignments to use the on-board J-Link as your serial bridge, see https://docs.nordicsemi.com/bundle/ug_nrf54lm20_dk/page/UG/nRF54LM20_DK/program_debug/virtual_serial_ports.html

Best regards,

Vidar

[VinayKotadamakki]

Hi Vidar, 

Yes we have external UART-USB Bridge which we have connected to PC and checking the output. But we are not able to see any logs printed on the console.

Please need your guidance on this.

Thanks and regards,

Vinay

[Vidar Berg]

Please try to include this kind of relevant information when posting a question. If you check the out the link I shared in my post here: https://devzone.nordicsemi.com/f/nordic-q-a/128250/nrf54lm20-i2c-communication-issue/566941, you can see that P1.02 is connected to the NFC antenna by default.

[VinayKotadamakki]

Hi Vidar,
Thank you for your info.

Sorry. Now I have changed the pinmux for UART20. Still I am not able to see any prints in my console.

Pinmux:

/ {
    aliases {
        uart0 = &uart20;
    };
};

&pinctrl {

    uart20_default: uart20_default {
        group1 {
            psels = <
                NRF_PSEL(UART_TX, 1, 2)
                NRF_PSEL(UART_RX, 1, 3)
                NRF_PSEL(UART_RTS, 1, 4)
                NRF_PSEL(UART_CTS, 1, 5)
            >;
            bias-pull-up;   // RX pull-up applied here
        };
    };

    uart20_sleep: uart20_sleep {
        group1 {
            psels = <
                NRF_PSEL(UART_TX, 1, 2)
                NRF_PSEL(UART_RX, 1, 3)
                NRF_PSEL(UART_RTS, 1, 4)
                NRF_PSEL(UART_CTS, 1, 5)
            >;
            low-power-enable;
        };
    };
};

&uart20 {
    status = "okay";

    current-speed = <115200>;

    pinctrl-0 = <&uart20_default>;
    pinctrl-1 = <&uart20_sleep>;
    pinctrl-names = "default", "sleep";
};

// / {
//     chosen {
//         zephyr,console = &uart21;
//         zephyr,shell-uart = &uart21;
//     };
// };

Application Sample using: Echo bot

External UART-USB is being used for checking the UART logs. 

Please let me know the issue.

Thanks and regards,

Vinay

[Vidar Berg]

Hi Vinay,

I see you are still using P1.02 for UART_TX, which as I mentioned in my previous reply, isn't connected to the pin header by default:

Is there a reason for why you cannot use the default pin assigments with the on-board Jlink serial bridge?

Regards,

Vidar

[VinayKotadamakki]

Hi Vidar,

Thank you for your reply.

Yes because we are using nRF54LM20 DK because we are going to build a custom board using nRF54LM20B. So we have used other pins for different usage. Ok I have tried this and still no output.

&pinctrl {
    uart20_default: uart20_default {
        group1 {
            psels = <
                NRF_PSEL(UART_TX, 1, 5)
                NRF_PSEL(UART_RX, 1, 6)
            >;
        };
    };

    uart20_sleep: uart20_sleep {
        group1 {
            psels = <
                NRF_PSEL(UART_TX, 1, 5)
                NRF_PSEL(UART_RX, 1, 6)
            >;
            low-power-enable;
        };
    };
};

&uart20 {
    compatible = "nordic,nrf-uarte";
    status = "okay";
    current-speed = <115200>;

    pinctrl-0 = <&uart20_default>;
    pinctrl-1 = <&uart20_sleep>;
    pinctrl-names = "default", "sleep";
};

Please let me know why I am facing this issue.

Thanks and regards,

Vinay