Digilent chipKIT Network Shield Podręcznik referencyjny - Strona 5
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2.2
USB Interface
The PIC32MX795 microcontroller on the Max32 contains a USB 2.0-compliant, full-speed device and On-The-Go
(OTG) controller. This controller has the following features:
USB full-speed host and device support
low-speed host support
USB OTG support
endpoint buffering anywhere in system RAM
integrated DMA to access system RAM and Flash memory.
Connector J4, on the top left side of the Network Shield, is a standard USB type-A receptacle. This connector is
generally used when the Max32/Network Shield has been programmed to operate as a USB host. The USB device is
connected to J4 either directly or via cable.
Connector J2, on the bottom left side of the Network Shield, is the Device/OTG connector. It is a standard USB
micro-AB connector. Connect a cable with a micro-A plug (available from Digilent) from this connector to a USB
port on a PC or USB hub.
When the USB controller in the PIC32 microcontroller on the Max32 board is in use, it takes over the use of several
of the pins. The signals provided by these pins appear on connector J13 on the Network Shield (connector J9 on
the Max32). Two additional signals are used when doing USB hosting. These signals appear on AN5 and digital pin
2. These pins are not available when using the USB interface.
When operating as a USB device, the chipKIT Max32/Network Shield will normally be a self-powered device. To
operate as a self-powered device, an external power supply should be connected to the external power connector
J2 on the Max32 board. If the external power supply is a regulated 5V supply, jumper JP1 on the Max32 should be
set in the BYP position to bypass the on-board 5V regulator.
The Max32/Network Shield can also be operated as a self-powered device powered by USB connector J1 on the
Max32. This is the connector used by the USB serial converter. When operated this way, the Max32/Network
Shield will be a bus-powered device from the perspective of the USB port connected to J1, and a self-powered
device from the perspective of the port connected to the USB connector J2 on the Network Shield.
Operation of the Max32/Network Shield as a bus-powered device is possible although not recommended in most
cases. The USB bus voltage from USB connector J2 appears on pin 1 of jumper JP4. Remove the shorting block from
JP4 and move the jumper from pin 1 to any point on the board that connects to the 5V VCC5V0 bus. The VCC5V0
bus can be accessed from power connector J17, pin 3. It can also be accessed from either pin of J14, the
uppermost two pins on the connector on the right edge of the board. When operating the board in this way, be
aware that if the USB serial converter on the Max32 is connected to a live USB port, the 5V power supplies of the
two USB ports (the one connected to the Max32 and the one connected to the Network Shield) will be shorted
together. If these are not the same power supply (i.e., both USB ports are on the same PC), one or both USB ports
and/or the Max32 or Network Shield may be damaged.
When operating as a USB host, the Max32/Network Shield should be externally powered. Connect a power supply
to the external power connector J2 on the Max32. If the external supply is a regulated 5V supply, place JP1 on the
Max32 in the BYP position to bypass the 5V regulator. The power supply must be able to supply enough current to
power both the Max32/Network Shield and the attached USB device, because the Max32/Network Shield provides
power to the attached USB device when operating as a host.
Copyright Digilent, Inc. All rights reserved.
Other product and company names mentioned may be trademarks of their respective owners.
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