Question

I bought a USB to Serial cable which claims to be CDC compliant.

But the bInterfaceClass value in interface descriptor is 0xFF(which is vendor specific). I was expecting it to be 0x02 (Communications and CDC control).

In the device manager, i found that the drivers being loaded are ser2pl.sys and serenum.sys. I had learnt usbser.sys is the windows CDC driver, but it was not loaded for my cable.

I am pretty much new to this CDC, so i have following questions

1.Does this indicate that the cable is not CDC compliant 2.Can i make this cable CDC compliant (since CDC is a driver functionality), by loading usbser.sys. If yes how?

Answer 1

I don t know for sure but thats indication that cable will not necessary follow CDC
I don t think you can make it compliant but if you want to use usbser.sys as driver for that cable you should provide inf file which should load usbser.sys if your cable is connected, check the driver VID PID etc probably this should help http://www.mjmwired.net/kernel/Documentation/usb/gadget_serial.txt (search for usbser.sys and look for .inf file, and modyfi it accordingly.

Answer 2

ser2pl.sys suggests a Prolific PL2303 device. They are not CDC compliant and they cannot be made to work with the CDC driver. OTOH they are working on Windows, Linux and OS X and are probably the most compatible chips on the market.

CDC was not used by cable vendors because it was really poorly implemented in Windows XP and IIRC it was not available at all in 9x/Me. It is nice that the driver finally work as it should in Windows 7 (dunno about Vista).

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