Cerebot MX7cK Reference Manual
www.digilentinc.com
page 7 of 34
Copyright Digilent, Inc. All rights reserved. Other product and company names mentioned may be trademarks of their respective owners.
Digilent Pmods are a line of small peripheral
modules that provide various kinds of I/O
interfaces. The Pmod product line includes
such things as button, switch and LED
modules, connector modules, LCD displays,
high current output drivers, various kinds of RF
interfaces, and many others.
There are two styles of Pmod connector: six-
pin and twelve-pin. Both connectors use
standard pin headers with 100mil spaced pins.
The six-pin connectors have the pins in a 1x6
configuration, while the twelve-pin connectors
use a 2x6 configuration. All of the Pmod
connectors on the Cerebot MX7cK are twelve
pin connectors.
Six-pin Pmod connectors provide four I/O
signals, ground and a switchable power
connection. The twelve-pin connectors provide
eight I/O signals, two power and two ground
pins. The twelve-pin connectors have the
signals arranged so that one twelve-pin
connector is equivalent to two of the six-pin
connectors. Pins 1–4 and 7–10 are the signal
pins, pins 5 and 11 are the ground pins and
pins 6 & 12 are the power supply pins.
The pin numbering that Digilent uses on the
twelve-pin Pmod connectors is non-standard.
The upper row of pins are numbered 1–6, left
to right (when viewed from the top of the
board), and the lower row of pins are
numbered 7–12, left to right. This is in keeping
with the convention that the upper and lower
rows of pins can be considered to be two six-
pin connectors stacked. When viewed from the
end of the connector, pin 1 is the upper right
pin and pin 7 is immediately below it (closer to
the PCB).
Each Pmod connector has an associated
power select jumper. These are used to select
the power supply voltage supplied to the power
supply pins on the Pmod connector. They are
switchable between either the unregulated
power supply, VCC5V0 or the 3.3V main board
supply, VCC3V3. Place the shorting block in
the 3V3 position for regulated 3.3V and in the
5V0 position to use the unregulated supply.
Each signal pin on the Pmod connectors is
connected to an input/output pin on the PIC32
microcontroller. Each pin has a 200 ohm series
resistor and an ESD protection diode. The
series resistor provides short circuit protection
to prevent damaging the I/O block in the
microcontroller if the pin is inadvertently
shorted to VDD or GND, or two outputs are
shorted together. The ESD protection diode
protects the I/O block from damage due to
electro-static discharge.
The 200 ohm resistor in series with each I/O
pin limits the amount of current that can be
sourced from the microcontroller pins. There
will be a 200mV voltage drop per mA of current
sourced by the pin. This will not be a problem
when driving typical, high impedance, logic
inputs, but can be problematic when trying to
drive low impedance inputs. If some cases, it
may be necessary to use external buffers
when trying to drive low impedance inputs.
Although ESD protection is provided between
the connector pins and the microcontroller
pins, ESD safe handling procedures should be
followed when handling the circuit board. The
pins on the microcontroller and other circuits
on the board are exposed and can be
damaged through ESD when handling the
board.
Digilent Pmod peripheral modules can either
be plugged directly into the connectors on the
Cerebot MX7cK or attached via cables.
Digilent has a variety of Pmod interconnect
cables available.
See the Pinout Tables in Appendix C, below,
for more information about connecting
peripheral modules and other devices to the
Cerebot MX7cK.
These tables describe the
mapping between pins on the PIC32MX795
microcontroller and the pins on the various
connectors.
The PIC32 microcontroller can source or sink a
maximum of 18mA on all digital I/O pins.
However, to keep the output voltage within the
specified input/output voltage range (V
OL
0.4V,
V
OH
2.4V) the pin current must be restricted to
