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USB CDC class on an embedded device

Posted: 08 Apr 2008 ?? ?Print Version ?Bookmark and Share

Keywords:communication device class? USB? embedded device?

The USB has made it very simple for end users to attach peripheral devices to a PC, all but eliminating the myriad of different interconnects that used to be necessary. One such interconnect that is becoming increasingly more rare is the RS-232 serial COM port. In fact, many modern laptop computers no longer have one. This can pose a challenge, for the developer needs a serial communication channel from a peripheral to a host PC.

Fortunately, a device can use the USB Communication Device Class (CDC) and allow the user to take advantage of the simplicity of the USB while providing the functionality of a COM port. The CDC is how communication devices interface to the USB. Intended for devices such as MODEMS and network interfaces, a subset of the CDC features can be used to emulate a serial port providing a "virtual" UART.

The overall flexibility and power of the USB requires managing protocols for device identification, configuration, control and data transfer. The Microchip PIC32 CDC serial driver handles the USB so the developer designing a device doesn't have to.

This document describes the Microchip PIC32 USB CDC serial driver and acts as a programmer's guide for developers wishing to adapt it to their own application. The CDC serial driver provides a simple "UART-like" firmware interface for transmitting and receiving data to and from the host, hiding most of the USB details away from the application. The sample code provided is easily customizable, reducing the amount of effort and learning that might otherwise be necessary when adding a USB interface to a device.

View the PDF document for more information.

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