Digilent 410-273P-KIT - Manual (Page 6)

WF32 Reference Manual
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Page 6 of 24
powered from the VCC3V3 bus. No circuitry on the WF32 board is powered from the VCC5V0 power bus, leaving
all current available from the 5V regulator to power external circuitry.
The POWER connector (J3) is used to power shields connected to the WF32 board. Pin 1 is unconnected, the
following pins are provided on this connector:
IOREF (pin 2): This pin is tied to the VCC3V3 bus.
P32_RST (pin 3): This connects to the MCLR pin on the PIC32 microcontroller and can be used to reset the PIC32.
VCC3V3 (pin 4): This routes the 3.3V power bus to shields.
VCC5V0 (pin 5): This routes the 5V power bus to shields.
GND (pin 6, 7): This provides a common ground connection between the WF32 and the shields. This common
ground is also accessible on connectors J4 and J5.
VEXT (pin 8): This connects to the voltage provided at the external power supply connectors (J14 and J17). This
can be used to provide unregulated input power to the shield. It can also be used to power the WF32 board from
the shield instead of from the external power connector.
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. The analog capable I/O pins are not 5V tolerant.
To provide 5V tolerance on those pins, the WF32 contains clamp diodes and current limiting resistors to protect
them from 5V input voltages.
The fact that all I/O pins are 5V tolerant means that it is safe to apply 5V logic levels to any pins on the board
without risk of damaging the PIC32 microcontroller.
The minimum high-voltage output of the PIC32 microcontroller is rated at 2.4V when sourcing 12mA of current.
When driving a high impedance input (typical of CMOS logic) the output high voltage will be close to 3.3V. Some 5V
devices will recognize this voltage as a logic high input, and some won’t. Many 5V logic devices will work reliably
with 3.3V inputs.
5 Input/ Output Connections
The WF32 board provides 43 of the I/O pins from the PIC32 microcontroller at pins on the input/output connectors
J6, J7, J8, J9, and J10.
The PIC32 microcontroller can source or sink a maximum of 25mA on all digital I/O pins. However, to keep the
output voltage within the specified output voltage range (V
OL
0.4V, V
OH
2.4V) the pin current must be restricted to
+7/-12mA. The maximum current that can be sourced or sunk across all I/O pins simultaneously is +/-200mA. The
maximum voltage that can be applied to any I/O pin is 5.5V although not all pins are 5V tolerant. For more detailed
specifications, refer to the PIC32MX5XX/6XX/7XX Data Sheet available from
www.microchip.com .