Is it possible to programmatically alter a USB<->Serial converter's 'BM' latency option?

Question

Is there any way to programmatically alter the 'BM Options Latency Timer' of a USB<->Serial adapter? Needs to work on embedded windows xp. Can be a .net 2.0 or native windows solution...

Answer 1

As of 2016, the advice in AN232B-04 may be outdated due to changes in the Windows driver infrastructure. Nowadays, there's a requirement to sign all files in a driver package, which means that editing values in a inf/cat file while otherwise using the stock FTDI driver is not possible without re-signing the driver.

If you're using libftdi, you can configure this value at runtime, as per rve's answer. If you prefer to use FTDI's own driver and Windows' standard COM port API, and you need to configure this value, you can still change it permanently and programmatically by editing the registry.

If you go this route, you need to change the DWORD value LatencyTimer under the key HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Enum\FTDIBUS\VID_0403+PID_6001+KBxxxxxxx\0000\Device Parameters. KBxxxxxxx in this example needs to be replaced by the serial number of your device. You would need higher privileges to change this value, eg by raising a UAC prompt. The device driver may need to be restarted at that point for the changes to take effect, for example by unplugging and replugging the device.

Answer 2

I think you are using an FTDI USB serial converter. Then you can use libftdi

And check out the Application Notes (especially AN232B-04) because they contain lots of useful information.

Answer 3

This is driver specific. Your best bet is to do what romkyns says and try to figure out where the driver stores this setting. You will probably need to close and reopen the serial port after changing the setting assuming you are able to find out how it is stored and are able to change it.