USB Device Classes
The Keil USB Device interface supports the Human Interface Device (HID), Mass Storage (MSC), Audio Device Class (ADC), the legacy serial port in the Communications Device Class (CDC), and a composite class.
HID - Human Interface Device
The Human Interface Device (HID) was originally used for USB mice and keyboards, however, it can be used to interface to any I/O device.
For an embedded system the HID driver can be used to pass control and configuration information between a host client and the application.
MSC - Mass Storage Class
Allows an external device to connect to the USB host and appear as a storage device, it is ideal for data aquisition and storage applications.
The USB device driver also provides all the necessary class support to link a host file system to the Flash file system via USB.
ADC - Audio Device Class
Allows you to stream audio data between the USB Host and the device as Isochronous packets.
Like the Mass Storage and HID classes, the Audio Class communicates with a standard driver within Windows.
CDC - Communications Device Class
This class implements a virtual serial port over USB, it is mainly used for modems, plain telephony applications, and can provide an interface for transmitting Ethernet or ATM frames.
Composite Device Class
Multi-function or compositie devices are easily supported by including the drivers for each of the required classes.