Port Mode: Host Device Port/File Path: COM1: Note the colon in COM1: (not semicolon). I have experienced the guest could become unstable without it. Also remember the IRQ and I/O Port settings. If another physical port than COM1 is to be used, change Port/File Path.
If the guest needs to have another port than COM1, set the Port Number to the required port. If using a user defined IRQ for the guest, IO APIC may have to be enabled. Blaupunkt Travel Pilot E here. Save the settings and start the guest. Open the Device Manager in the guest and go to the Ports (COM & LPT) section. If you see a COM3 port with a yellow warning icon skip the following section.
Connection through COM port between host and. In virtualbox, while virtualbox is running on windows 10 (host). I enabled serial port and chose host pipe in.