Specifications

V850E2/MN4 USB CDC (Communication Device Class) Driver
R01AN0010EJ0101 Rev.1.01 Page 10 of 117
Feb 01, 2012
3.2 Endpoints
An endpoint is an item of information used by the host device to identify a specific communication counterpart. An
endpoint is specified by a number from 0 to 15 and the direction (IN or OUT). An endpoint need be provided for each
data communication channel that is to be used by a peripheral device and cannot be shared by two or more
communication channels*
1
. For example, a device that has the capabilities to write and read to and from an SD card and
to print out data need be provided with an endpoint for writing to an SD card, an endpoint for reading from an SD card,
and an endpoint for sending data to a printer. Endpoint 0 is used for control transfer which must always be performed
by every device.
In data communication, the host device specifies the destination within the USB device using the USB device address
which identifies the device and an endpoint (number and direction).
A buffer memory is provided within every peripheral device as a physical circuit for endpoints. It also serves as a FIFO
that absorbs the difference in communication speed between the USB and the communication counterpart (e.g.,
memory).
Note: 1. There is a method of switching channels exclusively using a mechanism called the alternate setting.
3.3 Classes
Peripheral devices (function devices) connected via the USB have various classes defined according to their
functionality. Typical classes include the mass storage class (MSC), communication device class (CDC), and human
interface device class (HID). For each class, standard specifications are defined in the form of protocols. A common
host driver can be used provided that it conforms to those standard specifications.
The communication device class (CDC) is a class for communication equipment connected to a host computer. It is
used for devices such as modems, FAX equipment, and network cards. Since RS-232C interfaces are no longer
provided as standard equipment on personal computers, the CDC is often used for devices that implement USB serial
conversion when performing UART communication with a PC. Note that there are several models defined depending
on the mounted equipment. Of these, this sample driver uses the Abstract Control Model.