samples/boards/rpi_pico/uart_pio/boards/rpi_pico.overlay

&pinctrl {
	pio1_uart0_default: pio1_uart0_default {
		rx_pins {
			pinmux = <PIO1_P1>;
			input-enable;
			bias-pull-up;
		};
		tx_pins {
			pinmux = <PIO1_P0>;
		};
	};

	pio1_uart1_default: pio1_uart1_default {
		rx_pins {
			pinmux = <PIO1_P2>;
			input-enable;
			bias-pull-up;
		};
		tx_pins {
			pinmux = <PIO1_P3>;
		};
	};
};

&pio1 {
 	status = "okay";

	pio1_uart0: uart0 {
		pinctrl-0 = <&pio1_uart0_default>;
		pinctrl-names = "default";

		compatible = "raspberrypi,pico-uart-pio";
		current-speed = <115200>;
		status = "okay";
	};

	pio1_uart1: uart1 {
		pinctrl-0 = <&pio1_uart1_default>;
		pinctrl-names = "default";

		compatible = "raspberrypi,pico-uart-pio";
		current-speed = <115200>;
		status = "okay";
	};
};