Jetson Xavier NX unreadable pyserial (usb)

[veter-ochek]

I have 2 devices connected to Weighting terminal CAS-CI200A via RS-232:

• Lenovo notebook with Kubuntu 20.04 (x86_64 architecture)
• Jetson Xavier NX with Ubuntu 18.04 LTS, JetPack 4.5 (aarch64 architecture)

 import serial
    ser = serial.Serial(
        port='/dev/ttyUSB0',
        baudrate=9600,
        parity=serial.PARITY_EVEN,
        stopbits=1,
        bytesize=8
    )
    line = ser.readline()
    print(line)

Result of the same pyserial library for both devices is:

• for Lenovo: b'ERR 13\r\n'
• for Jetson: b'\x05\x1f\x12\x1f\x12\x1f\x1e\x1e\x0c\x06\r\n'

Also I try to use: cat /dev/ttyUSB0 results are the same.

Task is to get b'ERR 13\r\n' from Jetson.

I try to .decode() the line b'\x05\x1f\x12\x1f\x12\x1f\x1e\x1e\x0c\x06\r\n', but still no success:

The only difference between the devises is architecture and OS version, the library and the code are the same.

Does anyone know the way to get correct response?

[linuxdev]

@veter-ochek

via RS-232

Is this an actual 9-pin D-sub connector? If so, then the PHY voltages are wrong. This must be a 3.3V TTL level device (same protocol as RS-232, but different voltage levels).

[veter-ochek]

We use 9 pin D-sub RS232 to USB converter like this:

The voltage on usb power is 5.0 V
The voltage on usb signal is 2.9 V

[veter-ochek]

We found recommendation about usb process priority&governors: link.
Could you explain how to change process priority / USB power settings on Jetson Xavier (Jetpack)

[linuxdev]

The 9 pin D-sub you have could damage the Jetson, and is not suitable for use directly with the Jetson’s serial UARTs (you would have to use level converter hardware). You must use a 3.3V unit. Examples:
https://www.digikey.com/en/products/filter/smart-cables/468?s=N4IgjCBcpgbLVQGMoDMCGAbAzgUwDQgD2UA2iACxgAcAzAOwCsIAuoQA4AuUIAypwCcAlgDsA5iAC%2BhOPUQgUkDDgLEyIWgCZGFenLYguPfsPFTCFAJy15i5XkIlI5KtWrXWHbpD6DRE6RAAWghoBTQsBzVnEHpYalZAoJswxUEAV1UncjAABkTAzXV07AAjAAI8YSxy9PQBbhZJIA

Note that none of these use a 9-pin D-sub. All also have a spec of 3.3V. The 9-pin interface is the wrong PHY.

[veter-ochek]

I don’t connect usb to 9 pin D-sub directly, I use converter (cable on image) which base on chip PL2303SA. Also the same cable, as I wrote previously, work perfectly on laptop (Kubuntu 20.04).

[veter-ochek]

Found solution.

Problem was in converter’s driver(parity not work)
1a86:7523 QinHeng Electronics HL-340 USB-Serial adapter

The solution is to update driver.