Texas Instruments Technology for Innovators 4Q 2006 Скачать руководство пользователя страница 25

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Universal Serial Bus (USB)

The USB standard defines a bus product that
requires a host controller and enables plug-
and-play connectivity. The most recently
released final specification, USB 2.0, defines
high speed and allows complete backward
compatibility with USB 1.1.

USB products fall into three categories: hubs,
host controllers and peripherals. USB 1.1 sup-
ported speeds of up to 12 Mbps and cables
up to 5 meters long for these devices. USB
2.0 extends the connection speed to 480
Mbps to support next-generation peripherals
of higher-performance PCs and applications.
USB 2.0 officially defines three speeds: low
(1.5 Mbps), full (12 Mbps) and high (480
Mbps). The lowest speed is ideal for human
interface devices such as a mouse, game pad
or keyboard; while full speed is well suited
for “data dumps” to the PC via digital still
cameras, PDA cradles and flash-card readers.
Modems, printers, scanners and storage
drives are just a few of the items that can
take advantage of USB’s highest speed
specification.

The USB On-The-Go (OTG) supplement to USB
2.0 specifies a new class of devices aimed at
the portable market. USB OTG defines devices
that can operate as standard USB peripherals
when connected to a standard USB host
controller.

However, these same devices can operate
as reduced-function host controllers to
support selected USB OTG peripheral
devices. End-equipment manufacturers
can specify what type of peripherals their
devices will support when in OTG host
mode. This new specification allows easy
sharing of contact information between
USB OTG PDAs and cell phones or printing
of photographs directly from an OTG-
enabled digital still camera without a PC.

Technical Information

Speed

• The USB 2.0 standard defines three

speeds: low speed (LS) 1.5 Mbps, full
speed (FS) 12 Mbps and high speed (HS)
480 Mbps. It requires full backward and
forward compatibility for devices and

cables. All three modes offer both asyn-
chronous and isochronous (real-time) data
transmission over a simple and inexpensive
4-wire cable to meet requirements of
peripherals including keyboards, mice,
printers, speakers, scanners, external
storage devices and digital still cameras.

Transfer Type

• USB 2.0 defines four types of transfers:

bulk, control, interrupt and isochronous.
Bulk transfer is intended for applications
such as printers, scanners and mass
storage, where latency isn’t critical but
accuracy is. All devices must include
control transfers for configuration.
Interrupt transfer is for devices such as
mice, keyboards and game pads that must
receive the host’s or device’s attention
periodically. Isochronous transfer offers
guaranteed delivery time but no error-
checking or automatic retransmission of
data received with errors, making it the
better choice for audio or video applications.

Out

OUT

USB

Legacy

Serial

Peripheral

Host

(PC or OTG DRD)

TUSB3410

USB-to-Serial Bridge

The TUSB3410 provides an easy way to move a
serial-based legacy device to a fast, flexible
USB interface by bridging between a USB port
and an enhanced UART serial port. The
TUSB3410 contains all the necessary logic to
communicate with the host computer using the
USB bus.

Key Features

• USB full-speed-compliant: data rate of

12 Mbps

• 8052 microcontroller with 16 Kbytes of

RAM that can be loaded from the host
or from external onboard memory via an
I

C bus

• Integrated, enhanced UART features

including:

•

Programmable software/hardware flow
control

•

Automatic RS-485 bus transceiver
control, with and without echo