Digilent 410-302P-KIT - Manual (Page 6)

WiFire Reference Manual
LDO Out LDO In
VU 5V0
GND EN Ext
An external 5V regulator can be used. This would be desirable, for example, when operating from batteries. An
external switching mode 5V regulator could be used to provide higher power efficiency than the on-board linear
regulator. In this case, use wires as appropriate to connect VU to the unregulated input of the external regulator.
Connect the regulated 5V output to 5V0. Connect GND to the ground connection of the external regulator.
Optionally, connect EN Ext to the enable input control of the external regulator, if available. This allows the
external regulator to be turned off for low power operation. Digital pin 50 is then used to turn on/off the external
regulator.
The PIC32MZ microcontroller is rated to use a maximum of 60mA of current when operating at 200 MHz. The
MRF24WG0MA WiFi module typically consumes a maximum of 237mA when transmitting. This allows
approximately 303mA of current to power the remaining 3.3V circuitry on the WiFire board and external circuitry
powered from the VCC3V3 bus. No circuitry on the WiFire board is powered from the VCC5V0 power bus, leaving
all current available from the 5V regulator to power external circuitry and the USB 5.0V power bus when the
WiFire is used as a USB Host.
The POWER connector (J5) is used to power shields connected to the WiFire board. Pin 1 is unconnected, the
following pins are provided on this connector:
• IOREF (pin 2): This pin is tied to the VCC3V3 bus.
• RST (pin 3): This connects to the MCLR pin on the PIC32 microcontroller and can be used to reset the
PIC32.
• 3V3 (pin 4): This routes the 3.3V power bus to shields.
• 5V0 (pin 5): This routes 3.3V or 5.0V power to shields depending on the position of JP9.
• GND (pin 6, 7): This provides a common ground connection between the WiFire and the shields. This
common ground is also accessible on connectors J2 and J3.
• VIN (pin 8): This connects to the voltage provided at the external power supply connectors (J14 and
J15). This can be used to provide unregulated input power to the shield. It can also be used to power the
WiFire board from the shield instead of from the external power connector. If no power is supplied at
J14 or J15 or from the shield, VIN will not have any power on it.
4 5V Compatibility
The PIC32 microcontroller operates at 3.3V. The original Arduino boards operate at 5V, as do many Arduino
shields.
There are two issues to consider when dealing with 5V compatibility for 3.3V logic. The first is protection of 3.3V
inputs from damage caused by 5V signals. The second is whether the 3.3V output is high enough to be recognized
as a logic high value by a 5V input.
The digital I/O pins on the PIC32 microcontroller are 5V tolerant, whereas the analog capable I/O pins are not 5V
tolerant. There are 48 analog capable I/O pins on the PIC32MZ, and this applies to most GPIO pins on the
processor. Historically, clamp diodes and current limiting resistors have been used to protect the analog capable
I/O from being damaged; but because of the large number of analog capable I/Os, and because clamp diodes and
resistors will limit the maximum speed at which these I/Os will operate, it was decided that the WiFire would not
be 5V tolerant. Instead, JP9 was added to allow for the 5V0 bus to the shield to be selectable between 3.3V or
5.0V. If 5.0V is selected, great care must be used to ensure that no input to the PIC32MZ exceeds 3.6V; as that will
damage the PIC32MZ.
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