The maximum Baud rate achieveable with FTDI's current devices is 3M Baud.
This can be set or adjusted by setting a Baud rate divisor using the FT_SetDivisor function, or by setting the Baud rate directly with the FT_SetBaudRate function when using D2XX drivers. If using the FT_SetBaudRate function, the driver will select the nearest achieveable Baud rate to the one requested.
When using the FT_SetDivisor, the Baud rate divisor must be calculated using the following formula:
Integer Divisor + Sub-Integer Divisor = 3000000/Baud Rate
where the Integer Divisor is any integer between 2 and 16384 and the Sub-Integer Divisor can be any one of 0, 0.125, 0.25, 0.375, 0.5, 0.625, 0.75 or 0.875. Note that the FT8U232AM device will only support Sub-Integer Divisors of 0, 0.125, 0.25 and 0.5.
For a full description of achieveable Baud rates, please refer to the application note Configuring FT232BM Baud Rates on the Application Notes page of the FTDI website. This document is also relevant to FT2232C and FT8U232AM devices and also contains information on aliasing Baud rates for VCP drivers.
The following table provides an indication of the possible Baud rates. The blue boxes indicate special cases for the divisor values. The shaded boxes indicate the use of divisors not supported by the FT8U232AM device.