speed 115200, but
output is unreadable
Was it normal before? Suddenly the output is garbled?
You can check whether the serial cable and the board are loose, and restart the board.
com port on mother board - not work
usb-serial ftdi SI-ADA15061 - not work
usb-serial CH340 - work
The board UART ports uses 3.3V voltage levels. RS-232 ports have different voltage specifications and are not compatible:
Valid signals are either in the range of +3 to +15 volts or the range −3 to −15 volts with respect to the “Common Ground” (GND) pin