Digilent 410-302P-KIT - Manual (Page 10)

WiFire Reference Manual
this case, ensure that the total load does not exceed the 500mA maximum load that a USB device is allowed to
present to the host.
The USB host provides regulated 5V power to the connected USB device. The internal 5V LDO regulator can be
used to provide the USB power when operating from an external power supply. Place shorting blocks on jumper
block J17, as described above in the power supply section.
If the external power supply being used is a regulated 5V supply, place a shorting block between pins VU and 5V0
on connector J17, as described above in the power supply section to bypass the on board 5.0V regulator.
The power supply used must be able to supply enough current to power both the WiFire and the attached USB
device, since the WiFire provides power to the attached USB device when operating as a host. The USB 2.0
specification requires that the host provide at least 100mA to the device.
Jumper JP6 is used to provide the required USB host capacitance to the host connector being used. Place the
shorting block in the “A” position when using the standard USB type A (host) Connector (J12). Place the shorting
block in the “AB” position for use with the USB micro-AB (OTG) connector (J11).
With JP8 shorted, chipKIT pin 25 drives the enable input of a TPS2051B Current-Limited Power Distribution Switch
to supply 5V 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 chipKIT pin 8 (RA14/INT3) when JP7 is shorted. Details about the operation of the TPS2051B can be obtained
from the datasheet available at
www.ti.com .
When using the WiFire outside the MPIDE environment, the Microchip Harmony Library provides USB stack code
that can be used with the board. There are reference designs available on the Microchip website demonstrating
both device and host operation of PIC32 microcontrollers. These reference designs can be modified for developing
USB firmware for the WiFire.
9 SD Card Interface
The micro-SD card connector provides the ability to access data stored on micro-SD sized flash memory cards using
the SD card library provided as part of the MPIDE software system.
The SD card is accessed using an SPI interface on PIC32 microcontroller pins dedicated to this purpose. The MPIDE
SD library uses a “bit-banged” software SPI implementation to talk to SD card. However, software can be written to
access the SD card using SPI3.
On the WiFire board, SPI3 and I/O pins used to communicate with the SD card are dedicated to that function and
are not shared with other uses.
10 Peripheral I/O Functions
The PIC32 microcontroller on the WiFire board provides a number of peripheral functions. The provided
peripherals are explained in the following sections.
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