Digilent 410-173 User Manual

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Cerebot 32MX4 Circuit Diagram

Revision: August 26, 2011
Note: This document applies to REV C and REV D of the board.

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Overview

The Cerebot 32MX4 board is a useful tool for
embedded control and robotics projects for
both students and hobbyists.

Its versatile design and programmable
microcontroller lets you access numerous
peripheral devices and program the board for
multiple uses. The board has many I/O
connectors and power supply options.

The Cerebot 32MX4 works with the Microchip
MPLAB development environment and
provides built in programming and debugging
support under MPLAB.

The Cerebot 32MX4 provides a number of
connections for peripheral devices. It has nine
connectors for attaching Digilent Pmod™
peripheral modules. Digilent peripheral
modules include H-bridges, analog-to-digital
and digital-to-analog converters, speaker
amplifier, switches, buttons, LEDs, as well as
converters for easy connection to RS232,
screw terminals, BNC jacks, servo motors, and
more.

Features 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.

215 E Main Suite D | Pullman, WA 99163

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Cerebot 32MX4 Reference Manual

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

For more information on the
PIC32MX460F512L microcontroller, refer to
the PIC32MX3XX/4XX Family Data Sheet and
the PIC32 Family Reference Manual available
at www.microchip.com.

Functional Description

The Cerebot 32MX4 is designed for embedded
control and robotic applications as well as
microprocessor experimentation. Firmware
suitable for many applications can be
downloaded to the Cerebot 32MX4’s
programmable PIC32 microcontroller.

The board has a number of connection
options, and is specially designed to work with
the Digilent line of Pmod peripheral modules
with various input and output functions. For
more information, see www.digilentinc.com. In
addition to the Pmod connectors, the board
supports direct connection of up to 8 RC hobby
servos, provides two on-board push buttons
and four on-board LEDs for user i/o, as well as
providing connections for two I2C busses. A
serial EEPROM and a serial D/A converter are
provided on one of the I2C busses.

The Cerebot 32MX4 can be used with the
Microchip MPLAB development environment.
In-system-programming and debug of firmware
running on the PIC32 part is supported via
USB within MPLAB. The in-system-

programming and debug subsystem is
implemented in IC5, a PIC18LF4550
microcontroller. Access to this subsystem is
accomplished via USB connector J11.
Normally, J11 will be connected to an available
USB port on a PC while developing firmware to
run on the PIC32 microcontroller.

The Cerebot 32MX4 features a flexible power
supply routing system with a number of options
for powering the board as well as powering
peripheral modules 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 and In-System
Debug Using MPLAB

The Cerebot 32MX4 board is intended to be
use with the Microchip MPLAB IDE for
firmware development, programming and in­system debug. The board is compatible with
the Microchip PIC32 Starter Kit board, and
appears to MPLAB as a PIC32 Starter Kit.
When installing the MPLAB software, ensure
that the PIC32MX Starter Kit support is
installed.

After the MPLAB software is installed, the first
time that the board is used, Windows will need
to install the Microchip USB device driver to
connect to the board. If the “Found New
Hardware Wizard” asks for the installation CD
and no CD is available, click OK anyway. In
the “Files Needed” dialog box, use the browse
button to navigate to the folder: “Program
Files\Microchip\MPLAB
IDE\PIC32MXSkit\Drivers” and select the file:
mp32mxsk.sys and click on OK. The wizard
should then complete installing the proper
driver for the board. This process may need to
be repeated if the board is later connected to a
different USB port.

When creating a new project, ensure that the
device is set to PIC32MX460F512L. On the
Debugger.Select Tool menu, select the PIC32
Starter Kit as the debugger.

www.digilentinc.com page 2 of 15

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Cerebot 32MX4 Reference Manual

Board Power Supply

The Cerebot 32MX4 may be USB powered via
either the USB debug port, or the USB device
port. Alternatively, the board may be powered
via dedicated, “external”, power supply
connectors.

There are three different power supply
connectors on Cerebot 32MX4 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 supply 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.

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.

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.

The Cerebot 32MX4 is rated for external power
from 3.6 to 5 volts DC. Using voltage outside
this range could damage the board and
connected devices.

Connectors J13, J14, and J18 are wired in
parallel and connect to the “External Power”
position (center position) on the Power Select
jumper block J12. A shorting block should be
placed on the “External Power” 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 output of power select jumper block J12 is
wired to one terminal of the power switch,
SW1. The other terminal of SW1 connects to
the unregulated power bus DBG_VU. The
DBG_VU bus provides the input to the voltage
regulator powering the in-system-programming
and debug subsystem.

The Cerebot 32MX4 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 32MX4. This can be useful when
using servos that draw large amounts of
power.

Jumper JP1 can be used to connect the
Cerebot 32MX4 unregulated power bus VU to
the servo power bus, VS. When no shorting
block is installed on JP1, the VU and VS
busses are separate. When a shorting block is
on JP1, the two busses are joined and the VU
bus can be powered in any of the previously
indicated ways, or from connector J5.

The Cerebot 32MX4 can provide power to any
peripheral modules attached to the Pmod
connectors and to I2C devices powered from
the I2C daisy chain connectors, J2 and J6.
Each Pmod connector provides power pins
that can be powered by either unregulated
voltage, VU, or regulated voltage, VCC, by
setting the voltage jumper block to the desired
position. The I2C power connectors only
provide regulated voltage, VCC.

The PIC32 microcontroller and on-board I/O
devices operate at a supply voltage of 3.3V
provided by the VCC bus. The regulated
voltage on the VCC bus is provided by an on­board voltage regulator. This regulator is
capable of providing a maximum of 500mA of
current. 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. The
regulator is on the bottom of the board, near
the power connectors, and will get warm when

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Cerebot 32MX4 Reference Manual

the amount of current being used is close to its
limit.

Power Supply Monitor Circuit

The Cerebot 32MX4 microcontroller can
measure the power supply voltage on the 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 VU power, and
jumper JP2 enables the supply monitor circuit
for VS power. 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 VU and ADC
channel 9 is used to measure VS.

USB Operation

The PIC32MX460 microcontroller contains a
USB 2.0 Compliant, Full Speed Device and
On-The-Go (OTG) controller. This controller
provides the following features:

• USB full speed host and device support

• Low speed host support

• USB OTG support

• Endpoint buffering anywhere in system

RAM

• Integrated DMA to access system RAM
and Flash memory.

When operating as a USB device, the Cerebot
32MX4 can be used as a self powered device
or as a bus powered device. To operate as a
self powered device, an external power supply
should be connected to any one of the three
external power connectors (J13, J14, or J18)
and a shorting block placed on the center,
“External Power” position of J12. To operate

as a bus powered device, the shorting block
should be placed in the “USB Device Port”
position on J12.

Connector J15, on the bottom of the board in
the lower right corner is the Device/OTG
connector. This is a standard USB micro-AB
connector. Connect a cable with a micro-A
plug (optionally available from Digilent) from
this connector to an available USB port for
device operation.

When operating as a USB host, the Cerebot
32MX4 must be externally powered. Connect
a regulated 5V power supply to any one of the
three external power connectors (J13, J14, or
J18) and ensure that the shorting block is in
the center, “External Power” position of J12.
The power supply used must be a regulated
5V supply. The Cerebot 32MX4 board provides
power to the attached USB device when
operating as a host, and the USB specification
requires the use of a 5V power supply.

Jumper JP6 is used to route power to the host
connector being used. Place the shorting
block in the “Host” position for use with the
standard USB Host Connector, J17. Place the
shorting block in the “OTG” position for use
with the USB OTG connector, J15.

When operating as a USB host, the
PIC32MX460 microcontroller controls
application of power to the connected device
via the VBUSON control pin. A shorting block
must be placed in the “VBUSON” position of
J16 to enable this connection. With the
shorting block in place, bus power is applied to
the device by driving the VBUSON pin high.
Power is removed from the device by driving
the VBUSON pin low. The VBUSON pin is
accessed via bit 3 of the U1OTGCON register.

The VBUSON pin drives the enable input of a
TPS2051B Current-Limited Power Distribution
Switch to control the USB device power. This
switch has over-current detection capability.
The over-current output pin can be monitored
via the INT2/RE9 pin on the PIC32MX460
microcontroller. Insert a shorting block on JP5
to enable this connection. Details about the

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Cerebot 32MX4 Reference Manual

operation of the TPS2051B can be obtained
from the data sheet available at the Texas
Instruments web site.

There are reference designs available on the
Microchip web site demonstrating both device
and host operation of PIC32 microcontrollers.
These reference designs are suitable to use for
developing USB firmware for the Cerebot
32MX4 board.

Pmod Connectors

The Cerebot 32MX4 has nine Pmod
connectors for connecting Digilent Pmod
peripheral modules. 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.
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.
The power connection is switchable between
the regulated 3.3V main board supply and the
unregulated input supply.

Digilent Pmod peripheral modules can either
be plugged directly into the connectors on the
Cerebot 32MX4 or attached via cables.
Digilent has a variety of Pmod interconnect
cables available.

See the “Connector and Jumper Block Pinout
Tables” section below for more information
about connecting peripheral modules and other
devices to the Cerebot 32MX4. These tables
indicate the mapping between pins on the
PIC32MX460 microcontroller and the pins on
the various connectors.

RC Servo Connectors

The Cerebot 32MX4 provides eight 3-pin RC
hobby servo connectors for direct control of

servos in robotics and embedded hardware
actuator applications. The connectors share
I/O pins with Pmod connector JC. Individual
I/O pins may be accessed through the JC
connector if they're not in use by a servo.
Refer to the PIC32 family data sheet for
information on how to access the I/O pins.

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 (ideally timer 0)
to be used to control the signal timing for all
eight servo connectors.

The servo connectors on the Cerebot 32MX4
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
signal timing for the PWM signals to control RC
servos.

There are three power options for servo
connections: a common power bus (VU) for the
Cerebot 32MX4 and servos; separate on-board
power busses for the Cerebot 32MX4 (VU) and
the servos (VS); or an on-board power bus for
the Cerebot 32MX4 (VU) an external power
bus for servos.

For the first case above: Install the shorting
block on JP1 to connect the VS servo power
bus to the VU power bus. The servo power
bus is then powered from the same source as
the VU power bus. Powering a large number
of servos from USB power is not
recommended. USB power (J12 in the USB
Device Port, or USB Debug Port positions)
should only be used to power a couple of
servos to avoid exceeding the 500mA that a
USB device is allowed to use.

For the second case above: Remove the
shorting block from jumper JP2 to make the VS

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