USB communications device class (or USB CDC) is a composite

Universal Serial Bus Universal Serial Bus (USB) is an industry standard, developed by USB Implementers Forum (USB-IF), for digital data transmission and power delivery between many types of electronics. It specifies the architecture, in particular the physical ...

device class. The communications device class is used for

computer network A computer network is a collection of communicating computers and other devices, such as printers and smart phones. In order to communicate, the computers and devices must be connected by wired media like copper cables, optical fibers, or b ...

ing devices akin to a

network card A network interface controller (NIC, also known as a network interface card, network adapter, LAN adapter and physical network interface) is a computer hardware component that connects a computer to a computer network. Early network interface ...

, providing an interface for transmitting

Ethernet Ethernet ( ) is a family of wired computer networking technologies commonly used in local area networks (LAN), metropolitan area networks (MAN) and wide area networks (WAN). It was commercially introduced in 1980 and first standardized in 198 ...

or ATM frames onto some physical media. It is also used for

modem The Democratic Movement (, ; MoDem ) is a centre to centre-right political party in France, whose main ideological trends are liberalism and Christian democracy, and that is characterised by a strong pro-Europeanist stance. MoDem was establis ...

ISDN Integrated Services Digital Network (ISDN) is a set of communication standards for simultaneous digital transmission of voice, video, data, and other network services over the digitalised circuits of the public switched telephone network. ...

, fax machines, and

telephony Telephony ( ) is the field of technology involving the development, application, and deployment of telecommunications services for the purpose of electronic transmission of voice, fax, or data, between distant parties. The history of telephony is ...

applications for performing regular voice calls.

Microsoft Windows Windows is a Product lining, product line of Proprietary software, proprietary graphical user interface, graphical operating systems developed and marketed by Microsoft. It is grouped into families and subfamilies that cater to particular sec ...

versions prior to

Windows Vista Windows Vista is a major release of the Windows NT operating system developed by Microsoft. It was the direct successor to Windows XP, released five years earlier, which was then the longest time span between successive releases of Microsoft W ...

do not work with the networking parts of the USB CDC, instead using Microsoft's own derivative named Microsoft RNDIS, a serialized version of the Microsoft NDIS (Network Driver Interface Specification). With a vendor-supplied INF file, Windows Vista works with USB CDC and USB WMCDC devices. This class can be used for industrial equipment such as CNC machinery to allow upgrading from older

RS-232 In telecommunications, RS-232 or Recommended Standard 232 is a standard introduced in 1960 for serial communication transmission of data. It formally defines signals connecting between a ''DTE'' (''data terminal equipment'') such as a compu ...

serial controllers and robotics, since they can keep software compatibility. The device attaches to an RS-232 communications line and the operating system on the USB side makes the USB device appear as a traditional RS-232 port. While chip manufacturers such as Prolific Technology, FTDI,

Microchip An integrated circuit (IC), also known as a microchip or simply chip, is a set of electronic circuits, consisting of various electronic components (such as transistors, resistors, and capacitors) and their interconnections. These components a ...

, and Atmel manufacture USB chips and provide drivers that expose the chip as a virtual RS-232 device, the chips do not use USB CDC protocol and rather use their custom protocols, though there are some exceptions (PL2305PL-2305 USB to Printer Bridge Controller datasheet
/ref>). Devices of this class are also implemented in

embedded system An embedded system is a specialized computer system—a combination of a computer processor, computer memory, and input/output peripheral devices—that has a dedicated function within a larger mechanical or electronic system. It is e ...

s such as

mobile phone A mobile phone or cell phone is a portable telephone that allows users to make and receive calls over a radio frequency link while moving within a designated telephone service area, unlike fixed-location phones ( landline phones). This rad ...

s so that a phone may be used as a modem, fax or network port. The data interfaces are generally used to perform bulk data transfer.

References

External links

USB-IF's Approved Class Specification Documents

Class definitions for Communication Devices 1.2
(.zip file format, size 3.43 MB)
Class definitions for Communication Devices 1.1

App Note, ''Migrating from RS-232 to USB Bridge Specification''
Explains the use of USB CDC (Communications Device Class) ACM (Abstract Control Model) to emulate serial ports over USB.
PL2305I USB to Printer Bridge Controller (component data)
Communications device class {{compu-hardware-stub

See also

References

External links