Which kind of device are you communicating with ? USB doesn't work like a serial port: you don't have access directly to the port but instead you get the handle of a driver. This driver is shipped with the device you want to communicate with and manages all the communication with the device. To get the handle of the driver, simply call CreateFile supplying the correct driver name, then you should be able to use ReadFile and WriteFile. You can also do some more specific stuff by calling DeviceIOControl (in which you can pass some specific IO code which is dependent of your driver). So, if you want more help, you'll need to give a lot more information (which device do you try to access, if you have documentation with it, ...).
Cédric Moonen Software developer
Charting control [v1.2]