Digilent 410-302P-KIT - Manual (Page 9)

WiFire Reference Manual
8 USB Interface
The PIC32MZ microcontroller on the WiFire contains a USB 2.0 Compliant, Hi/Full-Speed Device and On-The-Go
(OTG) controller. This controller provides the following features:
• USB Hi or 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 J12 is a standard USB type A receptacle. This connector will be used when the WiFire has been
programmed to operate as a USB embedded host. The USB device is connected either directly to the WiFire, or via
cable to this connector.
Connector J11, on the bottom of the board, is the Device/OTG connector. This is a standard USB micro-AB
connector. Connect a cable with a micro-A plug (optionally available from Digilent) from this connector to an
available USB port on a PC or USB hub for device operation.
The USB specification allows for two types of devices with regard to how they are powered: self-powered devices
and bus powered devices. A self-powered device is one that is powered from a separate power supply and does
not draw power from the USB bus. A bus powered device is one that draws power from the USB bus and does not
have a separate power supply.
The WiFire can be operated as a self-powered device or as a bus powered device from either the USB serial
connector (J1) or the USB OTG/device connector (J11).
For operation as a self-powered device, place a shorting block on the EXT position of J16 and connect a suitable
external power supply to either J14 or J15.
To operate the WiFire as a bus powered device powered from the USB serial connector (J1), place a shorting block
in the UART position of J16. To operate as a bus powered device powered from the OTG/device connector (J11),
place a shorting block in the USB position of J16.
Note that there are two completely independent USB interfaces on the WiFire board, and it is possible for the
WiFire to appear as two different USB devices at the same time. These two devices can be connected to two
different USB ports on the same host, or to USB ports on two different hosts. If the WiFire board is connected to
two different USB hosts simultaneously, there will be a common ground connection between these two hosts
through the WiFire board. In this case, it is possible for ground current to flow through the WiFire board, possibly
damaging one or the other USB host if they do not share a common earth ground connection.
When the WiFire is operating as a bus powered device using USB connector J1, it will appear as a self-powered
device from the perspective of a USB host connected to J11. Similarly, when operating as a bus powered device
from connector J11, it will appear as a self-powered device from the perspective of connector J1.
A USB host is expected to be able to provide bus power to USB devices connected to it. Therefore, when operating
as a USB host, the WiFire should normally be externally powered. Connect a power supply to the external power
connector, J17. It is possible to operate the WiFire as a USB host powered from USB connector J1; however, in this
case the host USB port will be providing power for the WiFire as well as the USB device connected to the WiFire. In
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