Digilent MX4cK User Manual

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Revision: December 15, 2011
Note: This document applies to REV C of the board.

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Overview

The Cerebot MX4cK is a microcontroller
development board based on the Microchip
PIC32MX460F512L, a member of the 32-bit
PIC32 microcontroller family. It is compatible
with Digilent’s line of Pmod™ peripheral
modules, and is suitable for use with the
Microchip MPLAB® IDE tools. The Cerebot
MX4cK is also compatible for use with the
chipKIT™ MPIDE development environment.
ChipKIT and MPIDE is a PIC32 based system
compatible with many existing Arduino™ code
examples, reference materials and other
resources.

The Cerebot MX4cK is designed to be easy to
use and suitable for use by anyone from
beginners to advanced users for experimenting
with electronics and embedded control
systems. A built in programming/debugging
circuit compatible with the Microchip MPLAB®
IDE is provided on the board, so no additional
hardware is required for use with MPLAB. The
kit contains everything needed to start
developing embedded applications using either
the MPLAB® IDE or the MPIDE.

The Cerebot MX4cK provides 74 I/O pins that
support a number of peripheral functions, such
as USB controller, UART, SPI and I2C™ ports
as well as five pulse width modulated outputs
and five external interrupt inputs. Fifteen of the
I/O pins can be used as analog inputs in
addition to their use as digital inputs and
outputs.

The Cerebot MX4cK can be powered via USB,
or an external power supply that may be either
an AC-DC power adapter, or batteries.

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Cerebot MX4cK Circuit Diagram

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Cerebot MX4cK Reference Manual

Functional Description

The Cerebot MX4cK is designed for embedded
control and robotics control applications as well
as for general microprocessor experimentation.
Firmware suitable for many applications can be
downloaded to the Cerebot MX4cK’s
programmable PIC32 microcontroller.

Features of the Cerebot MX4cK include:

• a PIC32MX460F512L microcontroller

• support for programming and

debugging within the Microchip MPLAB
development environment

• nine Pmod connectors for Digilent
peripheral module boards

• eight hobby RC servo connectors

• USB 2.0 Device, Host, and OTG

support

• two push buttons

• four LEDs

• multiple power supply options, including

USB powered

• ESD protection and short circuit
protection for all I/O pins.

Features of the PIC32MX460F512L include:

• 512KB internal program flash memory

• 32KB internal SRAM memory

• USB 2.0 compliant full-speed On-The-

Go (OTG) controller with dedicated
DMA channel

• two serial peripheral interfaces (SPI)

• two UART serial interfaces

• two I2C serial interfaces

• five 16-bit timer/counters

• five timer capture inputs

• five compare/PWM outputs

• sixteen 10-bit analog inputs

• two analog comparators

The Cerebot MX4cK has a number of
input/output connection options, and is
specially designed to work with the Digilent
Pmod™ line of peripheral modules to provide a

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variety of input and output functions. For more
information, see www.digilentinc.com. In
addition to the Pmod connectors, the board
provides eight connectors for RC hobby
servos, two push button switches, and four
LEDs, as well as providing connections for two
I2C busses. A serial EEPROM and a 12-bit
digital to analog converter are provided on one
of the I2C busses.

The Cerebot MX4cK features a flexible power
supply system with a number of options for
powering the board as well as powering
peripheral devices connected to the board. It
can be USB powered via either the debug USB
port or the USB device port, or it can be
powered from an external power supply or
batteries.

Programming Tools

The Cerebot MX4cK can be used with either
the Microchip MPLAB® development
environment or the chipKIT MPIDE
development environment. When used with the
MPLAB IDE, in-system-programming and
debugging of firmware running on the
PIC32MX460 microcontroller is supported
using an on-board programming/debugging
circuit licensed from Microchip.

The Cerebot MX4cK is immediately useable
with either the MPLAB IDE or the chipKIT
MPIDE. No additional hardware is required to
use the board with the Microchip MPLAB tools.

Using the Cerebot MX4cK with
Microchip Development Tools

The Microchip MPLAB® IDE or the MPLAB® X
IDE can be used to program and debug code
running on the Cerebot MX4cK board using a
built-in programming/debugging circuit licensed
from Microchip.

The MPLAB programs can be freely
downloaded from the Microchip web site.
These software suites include a free evaluation

Cerebot MX4cK Reference Manual

copy of the Microchip C32 compiler for use
with the PIC32 microcontroller family. The
licensed debugger is compatible with the
MPLAB IDE version 8.63 or later.

When creating a new project, use the
“Configure.Select Device…” menu to specify the
PIC32 device being used. Ensure that the
device is set to PIC32MX460F512L.

In order to use the on-board program/debug
circuit it must be selected as the debugger or
programmer within the MPLAB IDE. Use the
“Debugger.Select Tool” menu, or the
“Programmer.Select Tool” menu, and select
“Licensed Debugger” as the programmer or
debugger.

The licensed debugger interface uses USB
connector J9, labeled DEBUG. Connector J9 is
a USB micro-B connector. Use a USB-A to
micro-B cable (provided with the board) to
connect to an available USB port on the PC.

When the licensed debugger is selected as the
programming or debugging device, the MPLAB
IDE will check the version number of the
firmware running on the debugger and offer to
update it if is out of date with the version of
MPLAB being used.

The in-system programming/debugging
interface uses two pins on the PIC32
microcontroller. The PIC32 devices support
two alternate pin pairs for this interface:
PGC1/PGD1 or PGC2/PGD2. PIC32 devices
use PGC2/PGD2 by default. The Cerebot
MX4ck is designed to use PGC2/PGD2. It is
not normally necessary to select the use of
PGC2/PGD2 for the debugging interface, as
this should occur automatically.

If for some reason, it is necessary to select the
correct pins for the programming/debugging
interface, this can done using configuration
variables set using the

#pragma config

statement. The following statement can be

used to configure the microcontroller for use
with the on-board licensed debugger circuit:

#pragma config ICESEL = ICS_PGx2

The MPLAB IDE may report an error indicating
that the device is not configured for debugging
until the first time a program is loaded onto the
board.

The MCLR pin on the PIC32 microcontroller is
used by the hardware programming/debugging
interface to reset the processor. This same pin
is used by the USB serial converter to reset the
processor when using the MPIDE. It is possible
that the reset function from the USB serial
interface can interfere with correct operation of
the Microchip programming and debugging
tools. If this happens, jumper JP8 can be used
to disconnect the USB serial converter reset
circuit. Remove the shorting block from JP8 to
disable the reset circuit. If the shorting block
has been removed, it is necessary to reinstall it
on JP8 in order to use the Cerebot MX4cK
board with the MPIDE again.

Using the Microchip development tools to
program the Cerebot MX4cK will erase the
chipKIT boot loader. To use the board with the
chipKIT MPIDE again, it is necessary to
program the boot loader back onto the board.
The programming file for the boot loader
programmed into the board by Digilent at the
factory is available for download from the
product page for the Cerebot MX4cK on the
Digilent web site. Additionally, the boot loader
source code is available in the chipKIT project
repository at www.github.com/chipKIT32/pic32-

Arduino-Bootloader.

To reprogram the boot loader using MPLAB,
perform the following steps:

• Use the “Configure.Select Device …” menu to
select the PIC32MX460F512L

• Use the “Programmer.Select Programmer”
menu to select the “Licensed Debugger”.

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Cerebot MX4cK Reference Manual

• Use the “File Import…” dialog box to
navigate to and select the boot loader
programming downloaded from the Digilent
web site. The file name will be something
like: chipKIT_Bootloader_MX4cK.hex

• Use the “Programmer.Program” command to
program all memories on the device.

Using the Cerebot MX4cK with the
chipKIT MPIDE

ChipKIT and the MPIDE is a PIC32 based
hardware and software system compatible

many existing Arduino™

code examples, reference
materials and other resources. The MPIDE
development platform was produced by
modifying the Arduino™ IDE and is fully
backward compatible with the Arduino IDE.
The Cerebot MX4cK board is designed to be
fully compatible with the chipKIT MPIDE
system, version 20111209 or later.

The MPIDE uses a serial communications port
to communicate with a boot loader running in
the target board. The serial port on the MX4cK
board is implemented using an FTDI FT232R
USB serial converter. Before attempting to use
the MPIDE to communicate with the MX4cK,
the appropriate USB device driver must be
installed.

The USB serial converter on the Cerebot
MX4cK board uses USB connector J8, labeled
UART on the board. This connector is a micro­USB. Use a standard USB-A to mini-B cable
(provided with the board) to connect the board
to an available USB port on the PC.

In the MPIDE, use the “Tools.Board” command
to select the Cerebot MX4cK from the list of
available boards. Use the “Tools.Serial Port”
command to choose the appropriate serial port
from the list of available serial ports on the PC.

When the MPIDE needs to communicate with
the MX4cK board, the PIC32 microcontroller is
reset and starts running the boot loader. The
MPIDE then establishes communications with

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with

the boot loader and downloads the program to
the board.

When the MPIDE opens the serial
communications connection on the PC, the
DTR pin on the FT232R chip is driven low.
This pin is coupled through a capacitor to the
MCLR pin on the PIC32 microcontroller.
Driving the MCLR line low resets the
microcontroller, restarting execution with the
boot loader.

Once the MPIDE has established
communication with the boot loader, it
transfers the user’s program to the boot loader,
which programs it into the flash memory in the
Microcontroller.

The automatic reset action when the serial
communications connection is opened can be
disabled. To disable this operation, remove the
shorting block from jumper JP8. The shorting
block is reinstalled on JP8 to restore operation
with the MPIDE.

Two red LEDs (LD7 and LD8) will blink when
data is being sent or received between the
Cerebot MX4cK and the PC over the serial
connection.

The header connector J7 provides access to
the other serial handshaking signals provided
by the FT232R. Connector J7 is not loaded at
the factory but can be installed by the user to
access these signals.

Additional Reference Documentation

For additional information about the Cerebot
MX4cK board and the use and operation of the
PIC32MX460F512L microcontroller, refer to
the following documents in addition to this
reference manual.

The Cerebot MX4cK Schematic, available on
the Cerebot MX4cK product page on the
Digilent web site: www.digilentinc.com

Cerebot MX4cK Reference Manual

The PIC32MX3XX/4XX Family Data Sheet and
the PIC32MX Family Reference Manual
available from the Microchip web site:

www.microchip.com

Additional reference material for the chipKIT
MPIDE system is included in the MPIDE
software download, and on-line in the chipKIT
wiki. Help with questions and problems using
the board with the chipKIT MPIDE software
can also be obtained in the chipKIT forums:

www.github.com/chipKIT32 (software

download)

www.chipKIT.org/wiki
www.chipKIT.org/forum

www.digilentinc.com page 5 of 35

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Cerebot MX4cK Reference Manual

Board Hardware Description

The following describes the various hardware
features of the Cerebot MX4cK board and the
PIC32XM460F512L microcontroller.

Power Supply

Switch SW1, in the lower left corner of the
board is the power switch. Place this switch in
the ON position to turn on board power and in
the OFF position to turn off board power.

The Cerebot MX4cK may be USB powered via
either the USB debug port, the USB UART
port, or the USB device port. Alternatively, the
board may be powered via dedicated,
“external”, power supply connectors.

Jumper block J12 is used to select the power
source used to provide power to the board.
This jumper block provides the following four
positions:

• USB – power is supplied by USB device
connector J15. This is used when the
Cerebot MX4cK is used to implement a
USB bus powered device.

• EXT – Power is supplied by one of the
external power connectors.

• DBG – Power is supplied by DEBUG USB
connector J9.

• URT – Power is supplied by UART USB
connector J8.

Place the shorting block in the appropriate
position on J12 for the desired power source
for the board.

The Cerebot MX4cK is rated for external power
from 3.6 to 12 volts DC. Using a voltage
outside this range could damage the board and
connected devices. If operating the board at a
voltage higher than 5V, it is necessary to
remove the shorting block on jumper JP10 to
protect the USB load switch, which is limited to
a maximum voltage of 5.5V. When operating

from any of the three USB sources, the input
voltage will be 5V.

The output of power select jumper block J12 is
connected to the VIN power bus. The VIN
power bus supplies power to Q3, a PFET load
switch, and IC9, the voltage regulator for the
licensed debugger circuit. The licensed
debugger circuit is powered as soon as the
power switch is turned on. Power to the rest of
the board is controlled by Q3. The main board
power supply is enabled by bringing the gate of
Q3 low. When Q3 is turned on, the unregulated
power bus BRD_VU is powered.

If the licensed debugger is connected to an
active USB port, it enumerates with the host
computer and once it has successfully been
enumerated, it turns on the main board power
supply by driving the PWR_ON signal high.

If the licensed debugger is not connected to an
active USB port, the PWR_ON signal is
ignored and board power is turned on
immediately by the power switch via transistor
Q4.

The main board power supply is a switch mode
voltage regulator implemented using a
Microchip MCP16301 switch mode step-down
regulator. This regulator provides 3.3V at up to
600 mA with approximately 96% efficiency.
This powers the main board regulated power
bus BRD_3V3

There are three connectors on Cerebot MX4cK
for connecting an external power supply: J13,
J14, and J18.

The barrel connector, J13, is useful for desktop
development and testing where using USB or
battery power is not suitable. J13 is the
connector used by the AC adapter optionally
available from Digilent, or other sources. J13
is a 2.5mm x 5.5mm coaxial connector wired
with the center terminal as the positive voltage.

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Cerebot MX4cK Reference Manual

Connector J14 is a two-pin male header that
provides easy battery or battery-pack
connection. Digilent has both two-cell and
four-cell AA battery holders with two pin
connectors available for connection to J14.

Connector J18 is a screw terminal connector
for an alternative power supply connection for
use with higher current battery packs, bench
supplies or other power sources where use of
a hard wired power supply is desirable.

Connectors J13, J14, and J18 are wired in
parallel and connect to the “External Power”
position on the Power Select jumper block J12.
A shorting block should be placed on the “EXT”
position of J12 when using this option for board
power. Only one of these three power
connectors should be used at a time. If
multiple power supplies are connected
simultaneously, damage to the board or the
power supplies may occur.

The Cerebot MX4cK has a second screw
terminal connector, J5 that supplies power to
the servo power bus, VS, to power the RC
hobby servo connectors. This allows servos to
be powered from a separate power supply than
the one powering the electronics on the
Cerebot MX4cK. This can be useful when
using servos that draw large amounts of
power.

Jumper JP1 can be used to connect the
Cerebot MX4cK unregulated power bus
BRD_VU to the servo power bus, VS. When
no shorting block is installed on JP1, the
BRD_VU and VS busses are separate. When
a shorting block is on JP1, the two busses are
joined and the BRD_VU bus can be powered
in any of the previously indicated ways, or from
connector J5.

The Cerebot MX4cK can provide power to any
peripheral modules attached to the Pmod

that can be powered by either unregulated
voltage, BRD_VU, or regulated voltage,
BRD_3V3, by setting the voltage jumper block
to the desired position. The I2C power
connectors only provide regulated voltage,
BRD_3V3.

The PIC32 microcontroller and on-board I/O
devices operate at a supply voltage of 3.3V
provided by the BRD_3V3 bus. The PIC32
microcontroller will use approximately 55mA
when running at 80MHz. The remaining
current is available to provide power to
attached Pmod and I2C devices.

Power Supply Monitor Circuit

The Cerebot MX4cK 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 Cerebot MX4cK with the
chipKIT MPIDE, these are accessed using the
analogRead() function using analog input A6 to
read BRD_VU and A7 to read VS.

connectors and to I2C devices powered from
the I2C daisy chain connectors, J2 and J6.
Each Pmod connector provides power pins

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Cerebot MX4cK Reference Manual

Pmod™ Connectors

The Cerebot MX4cK has nine connectors for
connecting Digilent Pmod peripheral modules.
The Pmod connectors, labeled JA–JF and JH–
JK, are 2x8 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: six­pin 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 MX4cK are twelve
pin connectors.

The six-pin 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 six­pin 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.

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 MX4cK or attached via cables.
Digilent has a variety of Pmod interconnect
cables available.

See the Pinout Tables in Appendix C, for more
information about connecting peripheral
modules and other devices to the Cerebot
MX4cK. These tables describe the mapping
between pins on the PIC32MX460
microcontroller and the pins on the various
connectors.

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Cerebot MX4cK Reference Manual

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 (VOL 0.4V,
VOH 2.4V) the pin current must be restricted to
+7/-12mA. The maximum current that can be
sourced or sunk across all I/O pins
simultaneously is +/-200mA. The maximum
voltage that can be applied to any digital I/O
pin is 5.5V. For more detailed specifications,
refer to the PIC32MX3XX/4XX Family Data
Sheet.

Digital Inputs and Outputs

The Cerebot MX4cK board provides access to
72 of the I/O pins from the PIC32
microcontroller via the Pmod connectors. Two
additional I/O pins can be accessed via the I2C
connector, J6. Any of the pins on the Pmod or
I2C connectors can be individually accessed for
digital input or output. Note that when the I2C
signals on J6 are being used for I2C
communications, they are not available for
general purpose I/O. Note that the signals on
I2C connector J2 are shared with pins 1 & 2 of
Pmod connector JF.

On PIC32 microcontrollers, the input/output
pins are grouped into I/O Ports and are
accessed via peripheral registers in the
microcontroller. There are seven I/O Ports
numbered A–G and each is 16 bits wide.
Depending on the particular PIC32
microcontroller, some of the I/O Ports are not
present, and not all 16 bits are present in all
I/O Ports.

Each I/O Port has four control registers: TRIS,
LAT, PORT, and ODC. The registers for I/O
Port A are named TRISA, LATA, PORTA and
ODCA. The registers for the other I/O Ports are
named similarly.

The TRIS register is used to set the pin
direction. Setting a TRIS bit to 0 makes the pin

an output. Setting the TRIS bit to 1 makes the
pin an input.

The LAT register is used to write to the I/O
Port. Writing to the LAT register sets any pins
configured as outputs. Reading from the LAT
register returns the last value written.

The PORT register is used to read from the I/O
Port. Reading from the PORT register returns
the current state of all of the pins in the I/O
Port. Writing to the PORT register is equivalent
to writing to the LAT register.

PIC32 microcontrollers allow any pin set as an
output to be configured as either a normal
totem-pole output or as an open-drain output.
The ODC register is used to control the output
type. Setting an ODC bit to 0 makes the pin a
normal output and setting it to 1 makes the pin
a open drain output.

Refer to the PIC32MX3XX/4XX Family Data
Sheet, and the PIC32 Family Reference
Manual, Section 12, IO Ports, for more detailed
information about the operation of the I/O Ports
in the microcontroller.

The chipKIT MPIDE system uses logical pin
numbers to identify digital I/O pins on the
connectors. These pin numbers start with pin 0
and are numbered up consecutively.

On the Cerebot MX4cK, pin numbers 0–71 are
used to access the pins on the Pmod
connectors and pin numbers 72 and 73 are
used for the two signal pins on the I2C
connector, J6. The pin numbers are assigned
so that connector JA pin 1 (JA-01) is digital pin
0, JA pin 2 (JA-02) is digital pin 1, and so on.

Pins 0-7 are on connector JA, pins 8-15 on JB,
pins 16-23 on JC, pins 24-31 and so on. Refer
to the tables in Appendix C for detailed
information about the pin mapping between
Pmod connector, logical pin number, and
PIC32 microcontroller pin number and pin
function.

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Cerebot MX4cK Reference Manual

When using the Cerebot MX4cK with the
chipKIT MPIDE the functions pinMode(),
digitalRead(), and digitalWrite() are used for
digital pin I/O.

The pinMode() function is used to set the pin
direction. Pin direction can be set to: INPUT,
OUTPUT, or OPEN. OPEN is used for open­drain and implies output.

The digitalRead() and digitalWrite() functions
are used to read or write the pins.
DigitalRead() returns the current state of the
specified pin, and digitalWrite is used to set the
state of an output pin. The pin state can be
either HIGH or LOW.

PIC32MX460 Pin 20

Pin 20 on the PIC32MX460 has multiple
functions. It provides the VBUSON signal when
the board is being used to implement a USB
host. It also provides the positive input for
analog comparator 1, analog to digital
converter input AN5, change notice interrupt
CN7 and bit 5 of general I/O Port B. In order to
support all of these different functions, jumper
block J16 is used to select the routing of this
pin.

Normally, the shorting block will be in the JJ-8
position. This connects microcontroller pin 20
to Pmod connector JJ pin 8. This allows the
use of most functions of this pin.

When the board is being used as a USB host,
the shorting block is placed in the VBUSON
position to allow use of the VBUSON signal to
control power to the USB bus.

Placing the shorting block in the DAC position
connects the output of IC3, the MCP4725
digital to analog converter to microcontroller
pin 20. This allows use of the DAC output to be
used as a programmable reference for analog
comparator 1.

Push Buttons and LEDs

The Cerebot MX4cK board provides two push
button switches for user input and four LEDs
for output. The buttons, BTN1 and BTN2 are
connected to I/O pins TRCLK/RA6 and
TRD3/RA7 respectively. To read the buttons,
pins 6 and 7 of I/O Port A must be set as
inputs by setting the corresponding bits in the
TRISA register. The button state is then
obtained by reading the PORTA register.
When a button is pressed, the corresponding
bit will be high (‘1’). Note that the
microcontroller pins used by the buttons are
shared with pins 3 & 4 of Pmod connector JF.

The four LEDs are connected to bits 10-13 of
I/O Port B. LED 1 is connected to bit 10, LED 2
is connected to bit 11, and so on. These four
bits are also shared with pins 1-4 of Pmod
connector JK. To use the LEDs, set the
desired bits as outputs by clearing the
corresponding bits in the TRISB register. The
state of an LED is set by writing values to the
LATB register. Setting a bit to 1 will illuminate
the LED and setting the bit to 0 will turn it off.

When using the MPIDE and the chipKIT
system, the buttons are accessed using
digitalRead() and the LEDs using digitalWrite().
Use the following pins to access them:

• BTN1 – PIN_BTN1, pin 42, RA6

• BTN2 – PIN_BTN2, pin 43, RA7

• LD1 – PIN_LED1, pin 64, RB10

• LD2 – PIN_LED2, pin 65, RB11

• LD3 – PIN_LED3, pin 66, RB12

• LD4 – PIN_LED4, pin 67, RB13

RC Servo Connectors

The Cerebot MX4cK provides eight 3-pin RC
hobby servo connectors, labeled S1-S8, for
direct control of servos in robotics and
embedded hardware actuator applications.
The connectors share the I/O pins with Pmod
connector JC. Individual I/O pins may be

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Cerebot MX4cK Reference Manual

accessed through the JC connector if they're
not being used to control a servo.

RC Servos use a pulse width modulated
signal, PWM, to control the servo position.
The 16-bit timers in the PIC32 microcontroller
have the ability to generate PWM signals using
the output compare registers. However, it is
also possible to use timer interrupts to
accomplish this same thing. Using timer
interrupts allows a single timer to be used to
control the signal timing for all eight servo
connectors.

The servo connectors on the Cerebot MX4cK
board are intended to be driven using timer
interrupts rather than directly by the pulse
width modulators in the internal timers. This
frees the pulse width modulators for other
uses, such as DC motor speed control.
Digilent has a reference design available that
illustrates using timer interrupts to control

• A common power bus (BRD_VU) for the
Cerebot MX4cK and servos

• Separate on-board power busses for the
Cerebot MX4cK (BRD_VU) and the servos
(VS)

• An on-board power bus for the Cerebot
MX4cK (BRD_VU) and an external power
bus for servos

For the first case above: Install a shorting
block on jumper JP1 to connect the VS servo
power bus to the BRD_VU power bus. The
servo power bus is then powered from the
same source as the BRD_VU power bus.
Powering a large number of servos from USB
power is not recommended. Pin header
jumpers and shorting blocks such as JP1 are
rated for a maximum of 2A of current. USB
power (J12 in the USB, DBG, or URT
positions) should only be used to power a
couple of servos to avoid exceeding the
500mA that a USB device is allowed to use.

signal timing for the PWM signals to control RC
servos.

When using the chipKIT MPIDE development
environment, the Servo library can be used to
drive servos attached to these connectors. The
symbols PIN_S1 through PIN_S8 can be used
to specify the servo connectors being used.

The following give the correspondence
between servo connector, MPIDE digital pin
number, and microcontroller I/O Port register
and bit position:

• S1 – PIN_S1, digital pin 16, RG12

• S2 – PIN_S2, digital pin 17, RG13

• S3 – PIN_S3, digital pin 18, RG14

• S4 – PIN_S4, digital pin 19, RG15

• S5 – PIN_S5, digital pin 20, RG0

• S6 – PIN_S6, digital pin 21, RG1

• S7 – PIN_S7, digital pin 22, RF0

• S8 – PIN_S8, digital pin 23, RF1

There are three options for supplying power to
the servo connections:

For the second case above: Remove the
shorting block from jumper JP2 to make the VS
servo power bus independent from the
BRD_VU bus. Attach the servo power supply
to screw terminal connector J5.

Finally, for very high servo current applications,
a separate power bus external to the Cerebot
MX4cK can be used to provide servo power. In
this case, remove the shorting block on JP1,
tie the external servo power bus ground to the
Cerebot MX4cK ground through the ground
terminal on J10, and use pin 1 on the servo
connectors to bring the servo control signals
out to the servos. The servo power and
ground connections are made off-board.

The on-board servo power bus can be used to
provide a maximum of 2A to each servo
connector and 5A total to all servo connectors.

5V Signal Compatibility

The PIC32 microcontroller operates at 3.3V.
And the I/O pins provide 3.3V logic levels. It is
possible, in some circumstances, to use the

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