Digilent chipKIT Network Shield Справочное руководство и руководство пользователя - Страница 6
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Печатать страницуchipKIT Network Shield Reference Manual
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
the 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 jumper from pin 1 to any point
on the board that connects to the 5V bus,
VCC5V0. 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/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
used must be able to supply enough current to
power both the Max32/Network Shield, and the
attached USB device, as the Max32/Network
Shield provides power to the attached USB
device when operating as a host.
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Jumper JP4 on the Network Shield is used to
route power to the host connector being used.
Place the shorting block in the "A" position
when using the standard USB type A (host)
Connector, J4. Place the shorting block in the
"MICRO" position for use with the USB micro-
AB (OTG) connector, J2.
When operating as a USB host, the
PIC32MX795 microcontroller controls
application of power to the connected device
via the VBUSON control pin (labeled VBUSON
in the schematic). Bus power is applied to the
USB bus by driving the VBUSON pin high.
Power is removed from the bus by driving the
VBUSON pin low. The VBUSON pin is
accessed via bit 3 of the U1OTGCON register.
The VBUSON signal is shared with same
microcontroller pin as analog input A5 and
digital pin 59.
The VBUSON pin drives the enable input of a
TPS2051B Current-Limited Power Distribution
Switch to control the application of USB power
to the host connector. This switch has over-
current detection capability and provides an
over-current fault indication by pulling the
signal USBOC low. The over-current output pin
can be monitored via the INT1/RE8 pin on the
PIC32MX795 microcontroller. This signal
appears on connector J14, pin 5 on the Max32
board, and is chipKIT digital pin 2. Details
about the operation of the TPS2051B can be
obtained from the data sheet available at the
Texas Instruments web site.
The VBUSON signal is shared with same
microcontroller pin as analog input A5 and
digital pin 59. This pin is not available for other
uses when operating as a USB host. If the
Max32/Network Shield is not being used as a
USB host, the use of A5/pin 59 can be
recovered by cutting the trace on the bottom of
JP3. USB Host capability can be restored by
soldering a two pin header to JP3 and
installing a shorting block.
The PIC32 USB controller can be accessed
using the chipKIT USB libraries for use within
the MPIDE environment.
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