FTDI have previously provided two types of driver for Windows: a D2XX direct driver and a virtual COM port (VCP) driver. Previously, these drivers were mutually exclusive and could not be installed at the same time. The new Windows combined driver model (CDM) allows applications to access FTDI devices through either the D2XX DLL or a COM port without having to change driver type. However, it should be noted that an application can only communicate through one of these interfaces at a time and cannot send commands to the D2XX DLL and the associated COM port at the same time.
The CDM driver comes in two parts. The bus layer provides D2XX style functionality and is always installed. The CDM driver will determine whether a COM port should be exposed by reading the EEPROM of FT232R, FT245R and FT2232C devices. In the case of FT232BM, FT245BM, FT8U232AM and FT8U245AM devices, the CDM driver will default to always installing a COM port. This behaviour can be changed and EEPROM settings ignored by changing the driver INF files as detailed in . Please note that modifying the INF files of a Microsoft WHQL certified driver will invalidate the certification.