Since the RtsEnable method of the SerialPort class can only be set with a BOOL value (two values of True/False), it cannot be set like the Win32API RTS_CONTROL_TOGGLE (0x3).
Therefore, the SerialPort class does not support half-duplex settings using the RTS output signal.
When performing half-duplex communication using the RTS output signal in the SerialPort class,
check the [Compulsion Half-Duplex] checkbox in the property settings via Device Manager.
With this change, [RTS_CONTROL_TOGGLE] is forcibly set to [fRtsControl] in the DCB structure.
Half-duplex communication is enabled even if [RTS_CONTROL_TOGGLE] is not specified in the program.