MX9 UART

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VAR-SOM-MX93 UART

UART Overview

UART Overview - VAR-SOM-MX93

The VAR-SOM-MX93 and DART-MX93 expose up to seven LPUART interfaces, some of which are multiplexed with other peripherals.

Serial Port	Device Node	Device Tree	VAR-SOM-MX93 / Symphony Board	DART-MX93 / DT8MCustomBoard
UART0	/dev/ttyLP0	lpuart1	Symphony board serial console	DT8MCustomboard serial console
UART2	/dev/ttyLP2	lpuart3	Disabled by default, see datasheet	Disabled by default, see datasheet
UART3	/dev/ttyLP3	lpuart4	Disabled by default, see datasheet	Disabled by default, see datasheet
UART4	/dev/ttyLP4	lpuart5	1.8V Signal level, used on SOM for Bluetooth interface and can be accessible only if Bluetooth is disabled.	1.8V Signal level, used on SOM for Bluetooth interface and can be accessible only if Bluetooth is disabled.
UART5	/dev/ttyLP5	lpuart6	Connected to Symphony board J18.7 and J18.9	Connected to DT8MCustomboard J12.4 and J12.6
UART6	/dev/ttyLP6	lpuart7	Connected to Symphony board J18.3 and J18.5	Connected to DT8MCustomboard J12.11 and J12.13
UART7	/dev/ttyLP7	lpuart8	Disabled by default, see datasheet	Disabled by default, see datasheet

Disabling Bluetooth / Enabling UART4 (/dev/ttyLP4)

UART4/ttyLP4 is used by the Bluetooth on the SOM. To use it on the carrier, Bluetooth must be disabled on the SOM.

First, disable variscite-bt by running:

# systemctl stop variscite-bt; systemctl stop variscite-ot
# systemctl disable variscite-bt; systemctl disable variscite-ot

Then, disable bluetooth in the device tree imx93-var-som.dtsi or imx93-var-dart.dtsi:

&lpuart5 {
   ...
	bluetooth {
		compatible = "nxp,88w8987-bt";
		status = "disabled";
	};
   ...
};

Testing UART5

The following demonstrates how to test UART5 on the VAR-SOM-MX93 Symphony board. The same process applies to the DT8MCustomboard following the table above.

Short J18.7 and J18.9 pins and run the following commands:

# stty -F /dev/ttyLP5 -echo -onlcr 115200
# cat /dev/ttyLP5 &
# echo hello > /dev/ttyLP5

For each invocation of echo command the "hello" string should appear on the terminal.

Testing UART6

The following demonstrates how to test UART6 on the VAR-SOM-MX93 / Symphony board. The same process applies to the DT8MCustomboard following the table above.

Short J18.3 and J18.5 pins and run the following commands:

# stty -F /dev/ttyLP6 -echo -onlcr 115200
# cat /dev/ttyLP6 &
# echo hello > /dev/ttyLP6

For each invocation of echo command the "hello" string should appear on the terminal.

Disabling UART5

To disable UART5 edit arch/arm64/boot/dts/freescale/imx93-var-som-symphony.dts or arch/arm64/boot/dts/freescale/imx93-var-dart-dt8mcustomboard.dts under kernel source directory and modify

&lpuart6 {
        ...
        status = "okay";
};

to

&lpuart6 {
        ...
        status = "disabled";
};

Other UARTs can be disabled in a similar manner by referencing the table above.

Configuring RS485 Half-Duplex

The i.MX93 supports controlling an rs485 transceiver driver enable using RTS_B. For more details, please refer to 63.3.4.4 Transceiver driver enable using RTS_B of the i.MX 93 Applications Processor Reference Manual.

RS485 is enabled in software by:

1. Enabling the RTS pin in the device tree.
2. Enabling RS485 in the serial driver.

The example below demonstrates how to do this on the VAR-SOM-MX93 using /dev/ttyLP6 on J18.3 (TX), J18.4 (RX) and J17.8 (RTS).

First, disable the ov5640_mipi0 which uses the RTS pin:

&ov5640_mipi0 {
	status = "disabled";
};

Then, configure the RTS pinmux in pinctrl_uart7:

 	pinctrl_uart7: uart7grp {
		fsl,pins = <
			...
			MX93_PAD_GPIO_IO11__LPUART7_RTS_B		0x31e
			...
		>;
	};

After booting the updated device tree, use the following python script to test RS485:

import sys
import serial
import serial.rs485
import time

def configure_rs485(port, data):
    try:
        # Open the serial port
        ser = serial.Serial(port, baudrate=9600)

        # Configure RS485
        ser.rs485_mode = serial.rs485.RS485Settings(
            delay_before_tx=0,
            delay_before_rx=0,
            rts_level_for_tx=False,  # RTS is low during transmission
            rts_level_for_rx=True,   # RTS is high during reception
            loopback=False
        )

        # Write data to the port three times with a delay of 10ms between each
        for _ in range(3):
            ser.write(data.encode())
            time.sleep(0.01)  # 10ms delay

        # Close the serial port
        ser.close()

        print("Data sent successfully.")

    except Exception as e:
        print(f"Error: {str(e)}")

if __name__ == "__main__":
    if len(sys.argv) != 3:
        print("Usage: python3 rs485.py <port> <data>")
    else:
        port = sys.argv[1]
        data = sys.argv[2]
        configure_rs485(port, data)

Finally, install pyserial and run the script:

root@imx93-var-som:~# pip3 install pyserial
root@imx93-var-som:~# python3 rs485.py /dev/ttyLP6 "hello"

The following image was captured on a logic analyzer using this example: