PIC32MX440F256H-80I Datasheet, PDF (280/646 Pages) Microchip Technology – 64/100-Pin General Purpose and USB 32-Bit Flash Microcontrollers

PIC32MX3XX/4XX
11.2 Operation
This section contains a brief overview of USB opera-
tion, followed by PIC32MX USB module implementa-
tion specifics, and module initialization requirements.
Note:
A good understanding of USB can be
gained from documents that are available
on the USB implementers web site. In par-
ticular, refer to the “Universal Serial Bus
Specification,
Revision
2.0”
(http://www.usb.org/developers/docs/).
11.3 USB 2.0 Operation Overview
USB is an asynchronous serial interface with a tiered
star configuration. USB is implemented as a mas-
ter/slave configuration. On a given bus, there can be
multiple (up to 127) slaves (devices), but there is only
one master (host).
There are three possible module modes of operation:
Host, Device, and OTG Dual Role.
11.4 Modes of Operation
The following USB implementation modes are
described in this overview:
• Host mode
- USB Standard Host mode – the USB imple-
mentation that is typically used for a personal
computer
- Embedded Host mode – the USB implemen-
tation that is typically used for a
microcontroller
• Device mode – the USB implementation that is
typically used for a peripheral such as a thumb-
drive, keyboard, or mouse
• OTG Dual Role mode – the USB implementation
in which an application may dynamically switch its
role as either host or device
11.4.1 HOST MODE
The host is the master in a USB system and is respon-
sible for identifying all devices connected to it (enumer-
ation), initiating all transfers, allocating bus bandwidth
and supplying power to any bus-powered USB devices
connected directly to it.
11.4.1.1 USB Standard Host
In USB Standard Host mode, the following features and
requirements are relevant:
• Large variety of devices are supported
• Supports all USB transfer types
• USB hubs are supported (allows connection of
multiple devices simultaneously)
• Device drivers can be updated to support new
devices
• Type ‘A’ receptacle is used for each port
• Each port must be able to deliver a minimum of
100 mA for a configured or unconfigured device,
and optionally, up to 500 mA for a configured
device
• Full-speed and low-speed protocols must be sup-
ported (high-speed can be supported).
Note: This mode is not supported by the
PIC32MX family.
11.4.1.2 Embedded Host
In Embedded Host mode, the following features and
requirements are relevant:
• Only supports a specific list of devices, referred to
as a Targeted Peripheral List (TPL)
• Only required to support those transfer types that
are required by devices in the TPL
• USB hub support is optional
• Device drivers are not required to be updateable
• Type ‘A’ receptacle is used for each port
• Only those speeds required by devices in the TLP
must be supported
• Each port must be able to deliver a minimum of
100 mA for a configured or unconfigured device,
and optionally, up to 500 mA for a configured
device
11.4.2 DEVICE MODE
USB devices accept commands and data from the host
and respond to requests for data. USB devices perform
peripheral functions, e.g., a mouse or other I/O, or data
storage.
The following characteristics generally describe a USB
device:
• Functionality may be class- or vendor-specific
• Draws 100 mA or less from the bus before config-
uration
• Can draw up to 500 mA from the bus after suc-
cessful negotiation with the host
• Can support low-speed, full-speed, or high-speed
protocol (high-speed support requires implemen-
tation of full-speed protocol to enumerate)
• Supports control and data transfers as required
for implementation
DS61143E-page 278
Preliminary
© 2008 Microchip Technology Inc.