CDC USB Devices
The Communication Device Class (CDC) supports a wide range of devices that can perform telecommunications and
networking functions.
Telecommunications devices → analog phones and modems, ISDN terminal adapters, digital phones, as well as COM-port
devices
Networking devices → ADSL and cable modems, as well as Ethernet adapters and hubs
The CDC implementation in the USB Component features:
•Emulation of a Virtual COM-port using the ACM (Abstract Control Model) subclass of CDC.
•Emulation of network connectivity using the RDNIS protocol using the ACM (Abstract Control Model)
subclass of CDC. This enables network connections over USB between a Windows host PC and an
embedded device, as well as USB Device RNDIS to Ethernet Bridge applications.
•Emulation of an Ethernet adapter using the NCM (Network Control Model) subclass of CDC (only available for
USB Device). Using CDC (NCM), you can create Ethernet-over-USB (for Linux hosts) applications on Linux-
based host systems.
Note
The following endpoint configurations are supported:
• One interrupt IN endpoint for notifications to the USB Host
• One bulk IN and one bulk OUT endpoint for data transfer
Smart card → Smart card readers and creating virtual smart card using USB
The latest PC/SC CCID specifications define a new smart card framework. This
framework works with USB devices with the specific device class 0x0B. Readers
with this class do not need device drivers when used with PC/SC-compliant
operating systems, because the operating system supplies the driver by default.
Content security → see Link
https://usb.org/sites/default/files/csm2_v1_0.pdf
CDC data → The communications device class is used for computer networking devices akin to a
network card, providing an interface for transmitting Ethernet or ATM frames onto
some physical media.
It is also used for modems, ISDN, fax machines, and telephony applications for
performing regular voice calls.
Billboard Device → USB 2.0 Billboard Device Class is defined to communicate the details of
supported Alternate Modes to the computer host OS.
It provides user readable strings with product description and user support
information.
Billboard messages can be used to identify incompatible
connections made by users. They are not required to negotiate Alternate
Modes and only appear when negotiation fails between the host (source) and
device (sink).
Despite its various functions, Type-C faces issues when connected to a non-
supporting device. This is where Billboard plays the key role as it instantly
informs users the issues.
What is Billboard?
First we need to understand the Type-C connection mode:
Alternate Mode: For example, PD, DisplayPort Alternate Mode (DP Alt Mode)
Billboard Device Class
When a device which supports Alternate Mode is connected to a non-
supporting host device, a pop-up window, or the Billboard, will show
information of the device status. Billboard notifies users the status of use
when the device does not support Alternate Mode.
When does Billboard show up?
When the device can correctly communicate and is recognized as an
Alternate Mode device, i.e., when a monitor that supports Type-C interface is
connecting via Type-C and the device manager is accurately recognized as a
monitor, the communication is then conducted in Alternate Mode with
images being displayed normally.
DIAGNOSTIC DEVICE → This base class is defined for devices that diagnostic devices. This
class code can be used in Device or Interface Descriptors.
Trace is a form of debugging where processor or system activity is
made externally visible in real-time or stored and later retrieved for
viewing by an applications developer, applications program, or,
external equipment specializing observing system activity.
Miscellaneous →
Machine Vision Device conforming to the USB3
USB3 Vision specification.
Vision
This standard covers cameras and other related
Control
devices that are typically used in machine vision,
Interface
industrial, and embedded applications.
Machine vision is the use of a camera or multiple cameras to inspect and analyze objects automatically, usually in an
industrial or production environment. The data acquired then can be used to control a process or manufacturing activity.
A typical application might be on an assembly line; after an operation is performed on a part, the camera is triggered to
capture and process an image.
Application specific →
