Supported Baud Rates for Older USB232 and USB485i

Baud Rates Supported by the Windows Drivers

For the older MEV USB232 and USB485i USB to serial converters, based on the FT8U232AM USB UART, the following baud rates are supported by the Windows drivers with an accuracy of 3% or better (typically better for lower baud rates). The ranges shown to the left outside the parentheses are the requested baud rates and the ranges shown to the right in parentheses are the corresponding extremes of the actually generated baud rates:

Baud Requested (Baud Generated)
184 - 386250 (184 - 375000)
388350 - 441428 (400000 - 428571)
448096 - 515000 (461538 - 500000)
529567 - 618000 (545455 - 600000)
647249 - 772500 (666667 - 750000)
832177 - 882856 (857143 - 857143)
896191 - 1030000 (923077 - 1000000)
1165049 - 1236000 (1200000 - 1200000)
1294499 - 1369863 (1333333 - 1333333)
1373878 - 1449275 (1411765 - 1411765)
1456311 - 1545000 (1500000 - 1500000)
2912622 - 3090000 (3000000 - 3000000)

If the Windows driver is requested to use a baud rate outside the above ranges, it will generally default to using a baud rate of 115200 (actually 115385). The following specified ranges are an exception to this rule due to faulty logic. The values shown to the right of the '=>' sign are the baud rates actually generated for the corresponding ranges specified on the left:

Baud Requested (Expected) Generated
1941747 - 2060000 (2000000) => 1000000 [2000000 / 2]
2330098 - 2472000 (2400000) => 600000 [2400000 / 4]
2600555 - 2758928 (2666666) => 333333 [2666666 / 8]

Custom Baud Rates in Windows Applications

Please see Setting USB232/485i Custom Baud Rates in Windows for more information about using custom baud rates in Windows applications.

Baud Rate Generation

The actual baud rates that the device can generate are given by the formula:

Baud = 3000000 / (N + F)

where N is any integer in the range 1 to 16383 and F has any of the following values: 0, 0.125, 0.25 or 0.5. However, the UART does not generate the correct baud rates if N = 1 AND F > 0.

Conversely, the formula may be reversed to produce integral and fractional parts of a baud rate divisor as follows:

N + F = 3000000 / Baud

However, note that the same constraints apply for valid values of N and F.

Latency and Data Throughput

FTDI's Application note AN232-04 discusses latency and data throughput issues for the FT8U232AM USB UART used by older versions of the USB232 and USB485i. Please note that the USB485i does not support hardware flow control.

On the USB side, the devices appear as "Full Speed" (12 Mbit/s) USB devices.

Updated Hardware

The new USB232U and USB232Ui devices are equivalent to the USB232 and USB485i, but use an updated USB UART - the FT232BM - and support additional baud rates. Please see Supported Baud Rates for USB232U and USB485Ui for details of the baud rates supported by these devices.