Specifications

V850E2/MN4 USB CDC (Communication Device Class) Driver
R01AN0010EJ0101 Rev.1.01 Page 9 of 117
Feb 01, 2012
3. USB Overview
This section provides a brief description of the USB standard to which the sample driver conforms.
USB (Universal Serial Bus) is a standard for interfacing various peripheral devices with a host computer with a
common connector. It provides an interface that is more flexible and easier to use than conventional interfaces. For
example, it supports the hot-plug feature and allows a maximum of 127 devices to be connected together through the
use of additional connection nodes called hubs. The ratio of the PCs having the USB interface installed to the entire PCs
that are presently available is reaching almost 100%. It can safely be said that the USB interface has become the
standard interface for connecting the PC and peripheral devices.
The USB standard is formulated and managed by the organization called the USB Implementers Forum (USB-IF). For
details on the USB standard, visit the USB-IF’s official web site (www.usb.org).
3.1 Transfer Modes
The USB standard defines four types of transfer modes (control, bulk, interrupt, and isochronous). The major features of
the transfer modes are summarized in table 3.1.
Table 3.1 USB Transfer Modes
Transfer Mode
Item
Control
Transfer Bulk Transfer
Interrupt
Transfer
Isochronous
Transfer
Feature
Transfer mode
that is used to
exchange
information
necessary for
controlling
peripheral
devices.
Transfer mode
that is used to
handle a large
amount of data
nonperiodically.
Transfer mode
that is used to
transfer data
periodically and
has a narrow
band width.
Transfer mode
used in
applications that
are required of
high realtime
performance.
High speed
(480 Mbps)
64 bytes 512 bytes 1 to 1024 bytes 1 to 1024 bytes
Full speed
(12 Mbps)
8, 16, 32, or 64
bytes
8, 16, 32, or 64
bytes
1 to 64 bytes 1 to 1023 bytes
Allowable
packet size
Low speed
(1.5 Mbps)
8 bytes — 1 to 8 bytes —
Transfer priority 3 3 2 1