Digilent 410-295P-KIT - Manual (Page 9)

ChipKIT Pro MX4 Reference Manual
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Page 9 of 37
3.1 Power Supply Monitor Circuit
The ChipKIT Pro MX4 microcontroller can measure the power supply voltage on the BRD_VU and VS power busses
using the provided power supply monitor circuits. This feature is especially useful when using batteries because it
allows the microcontroller firmware to determine the charge state of the battery and potentially notify the user
when a battery supply is low.
Each power supply monitor circuit is made up of a voltage divider that divides the power bus voltage by four, and a
filter capacitor to stabilize the voltage. Jumper JP4 enables the supply monitor circuit for BRD_VU power bus, and
jumper JP2 enables the supply monitor circuit for the VS power bus. The analog to digital converter built into the
PIC32 microcontroller is used to measure the power supply voltages. ADC channel 8 is used to measure BRD_VU
and ADC channel 9 is used to measure VS.
When using the ChipKIT Pro MX4 with the MPIDE, these are accessed using the analogRead() function using analog
input A6 to read BRD_VU and A7 to read VS.
4 Pmod Connectors
The ChipKIT Pro MX4 has nine connectors for connecting Digilent Pmod peripheral modules. The Pmod
connectors, labeled JA–JF and JH–JK, are 2x8 pin right-angle, female pin header connectors. Each connector has an
associated power select jumper block labeled JPA–JPF and JPH–JPK.
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 ChipKIT Pro MX4 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 pin on the Pmod connector. They are switchable between either the unregulated
power supply, BRD_VU, or the 3.3V main board supply, BRD_3V3. Place the shorting block in the 3V3 position for
regulated 3.3V and in the VU 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.