Installing Plug and Play Serial Ports and COM Ports
By default, the combined operation of the Ports class installer and the Serial function driver configure a serial port as a COM port. Serial creates a COM port device interface for a serial port if the SerialSkipExternalNaming entry value for a device does not exist or is set to zero. For more information about how Serial creates a COM port device interface for a COM port and how to override this operation, see External Naming of COM Ports.
The Ports class installer performs the following tasks when it installs a serial port:
Selects a COM port number and sets a port name in the PortName entry value under the device's hardware key. The port name has the format COM, where <n> is the port number. If Serial creates a COM port interface for the serial port, Serial uses the value of PortName as the symbolic link name for the COM port.
Displays a default property page dialog box, which allows a user to select settings for the port. For information about how to install a custom properties page, see Installing an Advanced Properties Page for a COM Port.
Sets the device friendly name for the device. You obtain the name using the SPDRP_FRIENDLYNAME flag with SetupDiGetDeviceRegistryProperty.
You can supply a co-installer to set registry settings for a Plug and Play serial device. If an entry value is not present in the registry, Serial uses a default value for the port.