Input/Output Connections - Digilent Wi-FIRE Reference Manual

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, 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 3.3Vv or 5.0Vv. If 5.0Vv is
selected, great care must be used to ensure that no input to the PIC32MZ exceeds 3.6Vv; as that
will damage the PIC32MZ.
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 WiFire 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 15mA on all digital I/O pins; however,
some pins can source or sink 25mA or even 33mA;, check with the PIC32MZ datasheet for more
information. To keep the output voltage within the specified output voltage range (VOL 0.4V, VOH
2.4V) the pin current must be restricted to +/-10mA on the 15mA pins, or for the higher current pins
check the PIC32MZ datasheet for the maximum currents. The maximum current that can be sourced
or sunk across all I/O pins simultaneously is +/-150mA. The maximum voltage that can be applied to
any I/O pin is 3.6V. For more detailed specifications, refer to the PIC32MZ Data Sheetdatasheet
available from
www.microchip.com.
Connectors J7 and J10 are 2×8 female pin header connectors that provide digital I/O signals. The
outer row of pins (closer to the board edge) corresponds to the I/O connector pins on an Arduino
Uno or Duemilanove board. The inner row of pins provides access to the extra I/O signals provided
by the PIC32 microcontroller.
Connector J8 is a 2×6 female pin header connector that provides access to the analog input pins on
the microcontroller. The outer row of pins corresponds to the six analog pins on an Arduino Uno or
Duemilanove. The inner row of pins is for the additional I/O signals provided by the PIC32
microcontroller. The analog pins on J8 can also be used as digital I/O pins.