LabVIEW
Window 7 through prolific USB to RS232, work with Modbus (watlow F4D)
Necroposting usually does not get the original poster to respond. We will need a bit more information about your hardware, and your code. Saying a db9 to usb converter narrows it down to essentially all of the usb serial adapters, really more helpful to tell us the brand, so that we might find which chip set it uses. Since lowering the "sample rate" seems to increase the time until it crashes a look at you serial code would help as well. You say you stopped the BSOD from happening, you were getting them? What did you change. My experience with usb serial devices is that Windows will change the COM port assignment (as mentioned in a previous post), particularly if you have either a flaky USB port (had that on an HP brand mini-desktop) or flaky USB extender. Windows sees it go away, then when it sees a "new" com port it assigns it a new number. BSOD are caused when the USB chip doesn't play nice with Windows. The instance I had of that was a vendor using a standard FTDI USB chipset, but wrapping the FTDI's dll in their own. Unfortunately it wasn't made "thread safe" so I would get random BSOD crashes. I convenienced the manufacturer to let me look inside their dll, wrote my own LabVIEW call to FTDI's dll (that was thread safe) that emulated how the manufacturer was talking to it and the problem went away. So, again, we need a bit more info.
So I believe the issue we are seeing here is that you are using some counterfeit prolific chips. Any cheap electronics now a days are being undercut and that usually means creating chips that appear as authentic as possible but aren't. The manufacturers of the legit hardware don't like this too well so they release an update that blocks counterfeit chips from working with their drivers. Customers are then confused why their hardware stops working with a driver update, or doesn't work at all. FTDI is another chipset that is quite common to get driver blocks, and even soft bricked some hardware with a driver update a while ago.
Here are some pages on the prolific counterfeit chips.
http://www.prolific.com.tw/US/ShowProduct.aspx?p_id=225&pcid=41
http://wp.brodzinski.net/hardware/fake-pl2303-how-to-install/
If this is your issue the solution is to uninstall all prolific drivers, and then only install an older version that didn't block these counterfeit chips. Beyond that I'd say support the official manufacturer and buy directly from them at a premium.
So it isn't so much that every brand uses the same core driver, as every manufacturer of counterfeit chips are using the same Prolific, or FTDI drivers. I know years ago we got 100 USB to RS-232 adapters from ebay that had no markings on them and were just generic FTDI devices. They were hand soldered, poor quality, and didn't work with the official drivers. Of course they were also something like $20 for the bundle of 100 so you get what you pay for.
