The USB-422 uses the FTDI chipset, this has been very reliable and has the advantage of well supported drivers for Windows, Mac and Linux.The only drawback of the standard FTDI driver is that it is shipped with a standard latency of 16 mSec which is long for RS422 control, especially at 29.97fps where one frame is only 33 mSec.
The data sheet shipped with the USB-422 includes details of how to reduce the latency and change the com port number for Windows applications, I have just modified this to suggest a latency setting of 1 or 2 mSec and not 4 mSec as before.
Latency adjustment for the Mac is more complicated as the driver must be modified and re-installed. To make this modification easier I have updated the USB-422 web page with a low latency driver and installation instructions.
http://www.colinbroad.com/cbsoft/usb422/usb422.html
