This usually means Windows does not have the vendor-specific driver and only has a generic PNP ID. Download the latest drivers from the card manufacturer's website or the Oxford chipset reference site. Ports Not Appearing or Wrong COM Numbers
The driver must implement an algorithm to calculate the divisor and prescaler values for the fractional baud rate generator. This requires more complex math than the simple integer division used in 16550A drivers to achieve non-standard or very high baud rates. 16c95x serial port driver
Even robust drivers can encounter issues. Here are typical problems and their solutions. This usually means Windows does not have the