Digilent Cerebot Plus Board User Manual
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Cerebot Plus Circuit Diagram
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Revision: 05/05/2008
Overview
The Digilent Cerebot Plus Board is a useful
tool for embedded control and robotics projects
for both students and hobbyists.
The Cerebot Plus Board’s versatile design and
programmable embedded microcontroller lets
you add different devices and program the
board for multiple uses. The board has many
I/O connectors and power supply options and
supports a number of programming options
including ATMEL AVR® STUDIO 4, and
WINAVR.
The Cerebot Plus has a number of connections
for peripheral devices. Digilent peripheral
modules include H-bridges, analog-to-digital
and digital-to-analog converters, a speaker,
switches, buttons, LEDs, as well as converters
for easy connection to RS232, screw terminals,
BNC jacks, servo motors, and more.
Features include:
• an ATmega2560 microcontroller
• 128KB expansion memory
• eight hobby RC servo connectors
• eleven Pmod connectors for Digilent
peripheral module boards
• an on-board voltage regulator
• multiple flexible power supply and
jumper options
• support for the Atmel AVRISP insystem programmer
• support for the Atmel AVR JTAGICE
mkII
• support for the Digilent Parallel and
USB AVR in-system programmers
• ESD protection for all I/O pins.
Various power
connectors
3.3V
regulator
256K Flash
(Internal)
4K EEPROM
(Internal)
8K SRAM
(Internal)
8
JA
Mem
Addr/
Data
JB
Mem
Addr
www. d i g i l e n t i n c . c om
215 E Main Suite D | Pullman, WA 99163
128K x 8
SRAM
A(16:8)
(509) 334 6306 Voice and Fax
User Input
Jumper
VCC
Addr
latch
AD(7:0)
GND
4 LEDs
8MHz
crystal
Reset
button
Digilent
ISP port
Ateml
ISP port
Ateml
ICE port
Internal
Oscillator
ATmega2560
TQ100
8 8 8 8 8 4 8
JC
Mem
Ctl
UART
JE
H-bridge
JD
SPI
TWI
UART
JF
H-bridge
Eleven Pmod connectors
H-bridge
LEDs
JG
&
8
JH
H-bridge
UART
JJ
Analog
&
JTAG
8
Analog
JK
8
UART, SPI,
&TWI ports
8
JL
UART
Eight servo
connectors
®
Doc: 502-129 page 1 of 13
Copyright Digilent, Inc. All rights reserved. Other product and company names mentioned may be trademarks of their respective owners.
Digilent Cerebot Plus Reference Manual Digilent, Inc.
Features of the ATmega2560 include:
• a serial peripheral interface (SPI)
• two USART serial interfaces
• ATMEL TWI serial interface
• eight 10-bit analog inputs
• two 8-bit timer counters
• two 16-bit timer counters
• 256KB program flash
• 4KB user EEPROM
• 4KB internal RAM
• an analog comparator.
Functional Description
The Cerebot Plus is designed for embedded
control and robotic applications as well as
microprocessor experimentation. Embedded
firmware suitable for many applications can be
downloaded to the Cerebot Plus board’s
programmable ATmega2560 microcontroller.
The Cerebot Plus has a number of connection
options, and is specially designed to work with
the Digilent line of peripheral modules (Pmods)
which provide various input and output
functions. For more information, see
www.digilentinc.com.
The Cerebot Plus has two programming
interface options: The Digilent in-systemprogramming option is accessed via connector
J1. A Digilent USB-JTAG/SPI cable or JTAG3
parallel programming cable can be attached to
connector J1. The Digilent AVR Programmer
application, available from the Digilent Web
site, can be used to program the board via the
Digilent programming cable. Alternatively, the
Atmel AVRISP in-system programmer can be
used. The AVRISP is connected to connector
J2 and programming is done using the Atmel
in-system-programming application built into
the Atmel AVR Studio software. The Cerebot
Plus also provides the ability to use the Atmel
AVR JTAG ICE mk-II debugging tool for
programming the board and debugging the
user firmware. The JTAG ICE is connected
using J6.
www.digilentinc.com page 2 of 13
Copyright Digilent, Inc. All rights reserved. Other product and company names mentioned may be trademarks of their respective owners.
The Cerebot Plus features a flexible power
supply routing system with a number of options
for powering the Cerebot Plus as well as
peripheral modules that connect to the board.
For more information on the ATmega2560
microcontroller, refer to the data sheet
available at www.atmel.com.
Pmod™ Connectors
The Cerebot Plus has eleven Pmod
connectors for connecting to Digilent Pmod
peripheral modules. There are two styles of
Pmod connector. The original Pmod connector
standard uses a six-pin-header style of
connectors providing four I/O signals, ground
and a switchable power connection. The power
connection is switchable between the
regulated 3.3V main board supply and the
unregulated input supply.
The newer Pmod connector standard uses a
12-pin (2x6) header connector and provides
eight signal pins, two grounds, and two
switchable power connections. The pin
arrangement is such that the new connector is
equivalent to two of the older connectors.
Digilent Pmod peripheral modules can either
be plugged directly into the connectors on the
Cerebot Plus or attached via cables. Digilent
has a variety of Pmod interconnect cables
available.
See the “Pmod Headers and SPI Connection”
section below for more information about
connecting peripheral modules and other
devices to the Cerebot Plus. It lists the header
connectors with their designed base function
and a mapping to the Atmega64L I/O register
ports. All pins can be used as general-purpose
digital I/O ports.
Power Supply Connectors
The Cerebot Plus may be powered via
dedicated power supply connectors, or it can
be powered through any of the board’s Pmod
connectors. The Cerebot Plus can also be
powered through the servo power connector.
Digilent Cerebot Plus Reference Manual Digilent, Inc.
The Cerebot Plus is rated for external power
from 3.6 to 9 volts DC. Using voltage outside
this range could damage the Cerebot Plus and
connected devices.
There are three different dedicated power
supply connectors on Cerebot Plus for board/
processor power: J7, J8, and J9.
The barrel connector, J7, is useful for desktop
development and testing where use of
batteries is cost- or time-prohibitive. J7 is the
connector used by the AC supply adapter
available from Digilent. J7 is a 2.5mm x 5.5mm
coaxial connector wired with the center
terminal as the positive voltage.
J8 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 J8.
J9 is a screw terminal connector for an
alternative battery supply or bench top power
supply connection.
Connectors J7, J8, and J9 are wired in parallel
and connect to one terminal of the power
switch, SW1. The other terminal of SW1
connects to the main unregulated power bus
VU. The VU power bus connects to the center
terminal of the voltage regulator input jumper
JP1 and also connects to the VU terminal of
the power select jumper associated with each
Pmod connector.
Jumper JP1 is used to select the voltage for
the main board power bus VCC. When JP1 is
in the ‘normal’ position, the VCC power bus is
powered by the output of the on-board 3.3V
regulator. When JP1 is in the ‘bypass’ position,
the on-board voltage regulator is bypassed and
the VCC bus is connected directly to the VU
bus. In this case, the AVR microcontroller and
other on-board electronics are powered directly
from the voltage supply connected to VU. In
this case, the input voltage must be in the
range 2.7V – 3.3V. A supply voltage outside
this range can permanently damage the board.
You can also power the Cerebot Plus from any
Pmod connector. Place the power select
jumper associated with the Pmod connector in
the VU position to supply power to the VU bus,
or the VCC position to supply power to the
VCC bus. If power is being supplied to the VU
bus, JP1 should be in the ‘normal’ position so
that the on-board regulator will be able to
regulate the supplied voltage to the 3.3V board
operating voltage. If the Pmod connector
power routing jumper is in the VCC position,
the shorting block on JP1 should be placed in
the ‘bypass’ position or removed.
The Cerebot Plus has a second screw terminal
connector, J10, 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 Plus. This can be useful when using
servos that draw large amounts of power.
The Cerebot Plus can provide power to any
peripheral modules attached to the Pmod
connectors and to TWI devices powered from
the TWI power daisy chain connectors, J4 and
J5. 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 TWI power connectors only
provide regulated voltage, VCC.
The regulated voltage on the VCC bus is
provided by an on-board voltage regulator.
This regulator is capable of providing a
maximum of 500mA of current. The
ATmega2560 microcontroller will use
approximately 15mA when running at 8MHz.
The external SRAM memory uses
approximately 90mA when operating and 1mA
when in standby mode. The remaining current
is available to provide power to attached Pmod
and TWI devices. The regulator is on the
bottom of the board, near the power
connectors, and will get warm when the
amount of current being used is close to its
limit.
www.digilentinc.com page 3 of 13
Copyright Digilent, Inc. All rights reserved. Other product and company names mentioned may be trademarks of their respective owners.
Digilent Cerebot Plus Reference Manual Digilent, Inc.
For information on how to set the jumper
blocks for VU and VCC, see Table 2.
Power Supply Monitor Circuit
The Atmega2560 microcontroller on the
Cerebot Plus 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 zener diode to clamp the
resulting voltage to no greater than 3.3V.
Jumper JP3 enables the supply monitor circuit
for VU power, and jumper JP4 enables the
supply monitor circuit for VS power. The
analog to digital converter built into the
ATmega2560 is used to measure the power
supply voltages. ADC channel 0 is used to
measure VU and ADC channel 1 is used to
measure VS.
When the power supply monitor circuit is
enabled the maximum safe voltage on VU is
9V and the maximum safe voltage on VS is
12V.
RC Servo Connectors
The Cerebot Plus 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 JJ on the lower
side of the board. Individual I/O pins may be
accessed through the JJ header if they're not
in use by a servo. Refer to the ATmega2560
data sheet for information on how to access
the I/O pins.
The I/O pins shared between the servo
connectors and connector JJ are also analog
to digital converter inputs on the ATmega2560
microcontroller. If servos are being driven on
www.digilentinc.com page 4 of 13
Copyright Digilent, Inc. All rights reserved. Other product and company names mentioned may be trademarks of their respective owners.
some channels and analog voltages are being
read on other pins simultaneously, it is
possible for digital switching noise to reduce
the accuracy of the analog to digital
conversions. If this is an issue, perform the
analog-to-digital conversions at times when the
servo pins are not switching. In normal
applications, there will be a great deal of dead
time when the servo pins are not switching.
There are three power options for servo
connections: a common power bus (VU) for the
Cerebot Plus and servos, separate on-board
power busses (VU and VS) for the Cerebot
Plus and servos, and an external power bus for
servos.
Install the shorting block on JP2 to connect the
VS servo power bus to the VU power bus. The
VU bus can be powered from the coax power
connector, J7, the screw terminal connector,
J9, or the 2-pin battery connector, J8.
The VU bus can also be powered from any of
the Pmod header interface connectors by
setting the corresponding power jumper block
to the VU position. This option is not suitable
for providing power for large numbers of
servos or servos that have a high current
demand.
Remove the shorting block from jumper JP2 to
make the VS servo power bus independent
from the VU bus. In this case, the VS bus is
powered from screw terminal connector J10.
Finally, for very high current applications, a
separate power bus external to the Cerebot
Plus can be used to provide servo power. In
this case, remove the shorting block on JP2,
tie the external servo power bus ground to the
Cerebot Plus 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.
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