Digilent MX7cK - Manual (Page 10)

Cerebot MX7cK Reference Manual
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The digital only I/O pins on the PIC32
microcontroller are 5V tolerant. It is safe to
apply 5V logic signals directly to these pins
without risk of damage to the microcontroller.
The analog capable I/O pins on the PIC32 are
not 5V tolerant. The absolute maximum
voltage rating for the analog pins is 3.6V.
Generally, the analog pins are the pins on I/O
port B, however, there are other non-5V
tolerant pins on the device.
Refer to the PIC32MX5XX/6XX/7XX Family
Data Sheet for more information about which
pins on the device are 5V tolerant before
applying input signals higher than 3.3V to any
pin on the Cerebot MX7cK board.
If a 5V signal is applied to a non-5V tolerant
pin, some external means must be used to limit
the applied voltage to 3.6V or less. The
Cerebot MX7cK board provides 200 ohm
series resistors between the microcontroller
pins and the Pmod connector pins. These
resistors are primarily intended to provide short
circuit protection on the outputs, but will also
provide limited protection if a 5V signal is
inadvertently applied to a non-5V tolerant pin.
One technique that can be used to limit an
input voltage to a safe level is to use a 200
ohm series resistor and Shottky diode
connected to the 3.3V supply to clamp the
voltage.
The minimum output high voltage 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 inputs will work reliably with 3.3V inputs.
If the 3.3V logic output is not sufficient for 5V
logic input to be reliably seen as a logic high
input signal, some external means must be
used to raise the output level. In some cases, a
pull-up resistor to 5V is sufficient. A pull-up
resistor in the range of 2Kohm
–10kOhm can
be used. This technique should not be used
with pins that are not 5V tolerant on the PIC32
microcontroller.
RESET
A reset button is at the upper right corner of
the board. Pressing this button will reset the
PIC32 microcontroller.