MX9 UART

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VAR-SOM-MX93 UART

VAR-SOM-MX93 UART Overview

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

Serial Port	Device Node	Device Tree	Note
UART0	/dev/ttyLP0	lpuart1	Connected to Symphony board serial console
UART2	/dev/ttyLP2	lpuart3	Disabled by default, see datasheet
UART3	/dev/ttyLP3	lpuart4	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 the variscite-bt Systemd service is disabled or SOM without "WBD" and "WB"
UART5	/dev/ttyLP5	lpuart6	Connected to Symphony board J18.7 and J18.9
UART6	/dev/ttyLP6	lpuart7	Connected to Symphony board J18.3 and J18.5
UART7	/dev/ttyLP7	lpuart8	Disabled by default, see datasheet

Testing UART5

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

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 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: