Chang,

> Can i find it on visual studio 5 msdn help?

I assume it's there too, I no longer have VS5 installed on any machine.

> Is it any problem using vfp to call DeviceIOContro() ?

There shouldn't be any problems calling the API function, it's pretty straightforward. But you are dealing with register settings so it's pretty easy to foul things up if you send the wrong stuff.

> Do you did it before?

No, I haven't worked on device I/O type applications in several years now, and never have under Windows.