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emUSB-Device CDC-NCM class

emUSB-Device Communication Device Class - Network Control Model (CDC-NCM) enables a USB device to act as a virtual network adapter. This can be used to run TCP/IP-based applications over USB.

  • Makes any TCP/IP application available using USB
  • No host driver needed for Linux or macOS



USB-based webserver

The most noteworthy application is a USB-based webserver. The USB webserver allows users to configure their device and to view data using a web browser. This saves development costs as there is no need to develop an application for every major operating system which would allow the user to interact with the USB device. The hardware costs can also be reduced as an Ethernet interface is not required.


Typical Applications

  • Router/gateway
  • USB to Ethernet adapter
  • Configuring a USB device using a web browser

Application Samples emUSB-Device CDC-NCM Class


USB to Ethernet Adapter




emUSB-Device CDC-NCM comes as a complete package and contains the following components:

  • CDC-NCM device class implementation
  • Network interface driver which uses emNet as a TCP/IP stack
  • A sample application demonstrating how to work with CDC-NCM  

The CDC-NCM Class is a standard USB class protocol defined by the consortium.
A TCP/IP stack like emNet is required on the USB device side to handle the actual IP communication.
Any available IP protocol (UDP, TCP, FTP, HTTP, etc.) can be used to exchange data.

Linux kernel versions newer than 2.6.38 have full support for CDC-NCM. 
macOS has full support for CDC-NCM.
For Windows a CDC-NCM driver is required.

One Bulk IN, one Bulk OUT and one Interrupt IN endpoint are required for emUSB-Device CDC-NCM.

emUSB-Device CDC-NCM can be used in combination with other interfaces (Bulk, CDC, MSD, MTP, HID) without any issues.

On a typical Cortex-M CPU running at 120MHz a transfer speed of about 5 MByte/sec can be achieved when using a high-speed USB connection.

Components required to use CDC-NCM:

  • emUSB-Device core
  • emUSB target driver
  • emNet (IP stack)