Devices that use the abstract control model include virtual COM ports and
Ethernet devices that comply with the Microsoft-specific Remote NDIS protocol.
The Remote NDIS USB Driver Kit, available from Microsoft, includes
Microsoft??™s specification.
The CDC telephone control model supports call management and notifications
and typically uses other classes such as audio for data and HID for a keypad
interface.
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The function performed by Virtual COM-port devices is sometimes called
serial emulation. The CDC specification says that abstract-control-model
devices understand AT commands. In practice, however, a vitual COM-port
device that doesn??™t communicate with a modem that uses the commands will
never receive a command and thus doesn??™t need to support them.
A generic COM-port device that supports the abstract control model and uses
the standard Windows drivers performs these tasks:
??? Returns descriptors that identify the device as a COM-port device that supports
the abstract control model and common AT commands.
??? Accepts COM-port data on a bulk OUT endpoint.
??? Sends COM-port data as needed on a bulk IN endpoint.
??? Sends SERIAL_STATE notifications as needed on an interrupt IN endpoint.
In addition, most abstract control model devices support class-specific requests
to get and set asynchronous port parameters and to control the RS-232 signals
RTS, DTR, and Break.
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