There may be multiple USB devices in any system such as joysticks, speakers, printers,
etc. USB devices present a standard USB interface in terms of comprehension, response,
and standard capability.
The host initiates transactions to specific peripherals, whereas the device responds to
control transactions. The device sends and receives data to and from the host using a
standard USB data format. USB 2.0 full-speed /low-speed peripherals operate at 12Mbit/s
or 1.5 Mbit/s.
For additional information, see the USB 2.0 specification.
External Hub
Root
Hub
USB Cable
USB Cable
USB Cable
External Hub
USB Peripherals
Host PC
Host
Software
USB Cables
Figure 42-1. Example USB 2.0 system configuration
42.1.2 USB On-The-Go
USB is a popular standard for connecting peripherals and portable consumer electronic
devices such as digital cameras and tablets to host PCs. The On-The-Go (OTG)
Supplement to the USB Specification extends USB to peer-to-peer application. Using
USB OTG technology, consumer electronics, peripherals, and portable devices can
connect to each other to exchange data. For example, a digital camera can connect
directly to a printer, or a keyboard can connect to a tablet to exchange data.
With the USB On-The-Go product, you can develop a fully USB-compliant peripheral
device that can also assume the role of a USB host. Software determines the role of the
device based on hardware signals, and then initializes the device in the appropriate mode
of operation (host or peripheral) based on how it is connected. After connecting, the
devices can negotiate using the OTG protocols to assume the role of host or peripheral
based on the task to be accomplished.
Introduction
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Freescale Semiconductor, Inc.