Digilent 410-273P-KIT Manuel d'utilisateur télécharger pdf (Page 9)

WF32 Reference Manual

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Page 9 of 24

The WF32 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 (J12). As described in the power supply section above, jumper

block (J15) is used to select the power source to be used to power the board.

For operation as a self-powered device, place a shorting block on the EXT position of J15 and connect a suitable

external power supply to either J14 or J17.

To operate the WF32 as a bus powered device powered from the USB serial connector (J1), place a shorting block

in the UART position of J15. To operate as a bus powered device powered from the OTG/device connector (J12),

place a shorting block in the USB position of J15.

Note that there are two completely independent USB interfaces on the WF32 board, and it is possible for the

WF32 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 WF32 board is connected to

two different USB hosts simultaneously, there will be a common ground connection between these two hosts

through the WF32 board. In this case, it is possible for ground current to flow through the WF32 board, possibly

damaging one or the other USB host if they do not share a common earth ground connection.

When the WF32 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 J12. Similarly when operating as a bus powered device

from connector J12, 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 WF32 should normally be externally powered. Connect a power supply to the external power

connector, J17. It is possible to operate the WF32 as a USB host powered from USB connector J1, however in this

case, the host USB port will be providing power for the WF32 as well as the USB device connected to the WF32. In

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 J16 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 J16 as described above in the power supply section.

The power supply used must be able to supply enough current to power both the WF32, and the attached USB

device, since the WF32 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 JP10 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 (J13). Place the shorting block in the “AB” position for use

with the USB micro-AB (OTG) connector (J12).

When operating as a USB host, the PIC32MX695 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 A. When operating as a USB host, this pin is not available as an analog input or general purpose I/O pin.

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Digilent 410-273P-KIT Manuel d'utilisateur Page 9