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Ignore Hardware Serial Number
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If devices have the same vendor ID and product ID but different serial numbers, the system will normally treat them as different devices. This causes the drivers to be installed for each device and create registry entries for each device.

It is possible to override this behaviour to make the system ignore a device's serial number and treat all devices with matching VID and PID connected to the same USB port as if they were the same device. This is achieved by adding a REG_BINARY value called
to the registry and setting it to 01.

This value is held in the registry key located at:

   HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\UsbFlags\IgnoreHWSerNum{Device VID, PID and interface}

For a default FTDI device ID (VID 0x0403, PID 0x6001), add the following registry REG_BINARY value set to 01:


For port A of an FT2232 device with default VID and PID, the IgnoreHWSerNum string would be:


and for port B of an FT2232 device the IgnoreHWSerNum string would be:


As the FT2232 device also uses the Windows composite device driver, an additional IgnoreHWSerNum entry is required to prevent Windows from creating additional composite driver registry entries:


Now the system can treat devices with the same vendor ID and product ID but different serial numbers as the same device and drivers are installed for the first device only. As such, only one entry is created in the registry. If the device is connected to another USB port, the driver will have to be reinstalled for that port.

Note that IgnoreHWSerNum cannot be setup in FTDIBUS.INF or FTDIPORT.INF, it must be setup by editing the registry manually or by an installation utility BEFORE installing the driver.