Digilent chipKIT Pro MX7 Reference Manual page 7

chipKIT™ Pro MX7 Board Reference Manual
2.1 RESET
A reset button is at the upper right corner of the board. Pressing this button will reset the PIC32 microcontroller.
3 Pmod Ports
The chipKIT Pro MX7 has six connectors for connecting Digilent Pmods. The Pmod ports labeled JA–JF, are 2x6 pin,
right-angle, female pin header connectors. Each connector has an associated power select jumper block labeled
JPA–JPF.
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 port: six-pin and twelve-pin. Both connectors use standard pin headers with 100mil
spaced pins. The six-pin ports have the pins in a 1x6 configuration, while the twelve-pin ports use a 2x6
configuration. All of the Pmod ports on the chipKIT Pro MX7 are twelve pin connectors.
Six-pin Pmod ports provide four I/O signals, ground and a switchable power connection. The twelve-pin ports
provide eight I/O signals, two power pins, and two ground pins. The twelve-pin ports have the signals arranged so
that one twelve-pin port is equivalent to two of the six-pin ports. 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 ports 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 ports 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 port has an associated power select jumper. These are used to select the power supply voltage
supplied to the power supply pins on the Pmod port. 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 ports are 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. In 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.
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