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AN39: USB Interface Description

3.3 Composite Device Interfaces for "Mdm" Enumeration

HC15_USB_Interface_v02 Page 11 of 28 2007-04-05

Confidential / Preliminary

3.3 Composite Device Interfaces for "Mdm" Enumeration

3.3.1 Interfaces 0 and 1 (CDC ACM MODEM Port)

This port is mainly intended for dialup data connections. It implements a standard legacy

modem protocol. The port consists of two USB interfaces. One interface serves as CDC ACM

control interface, the other one as CDC ACM data interface.

3.3.1.1 Interface 0 (CDC ACM – Control)

Interface 0 has only one endpoint:

• Interrupt IN notification endpoint

The MODEM notification endpoint is also used for notifications from VCOM1 port (see Section

3.3.2). Therefore, an USB host driver must evaluate the notification interface number.

3.3.1.2 Interface 1 (CDC ACM – Data)

Interface 1 has two endpoints:

• Bulk-only data IN

• Bulk-only data OUT

3.3.2 Interface 2 (VCOM1 Port)

Interface 2 has two endpoints:

• Bulk-only data IN

• Bulk-only data OUT

The interface serves as so-called application port and supports AT commands as specified in

[1]

or [2], but no data connections.

3.3.3 USB Interface 3 (VCOM2 Port)

Interface 3 has two endpoints:

• Bulk-only data IN

• Bulk-only data OUT

Interface 3 is only enumerated. It is reserved for possible future use.

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Siemens HC15 User Manual Page 11