Digilent Cerebot II Board - Manual (Page 5)

Cerebot II Reference Manual Digilent, Inc.
www.digilentinc.com page 5 of 10
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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 II
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 II 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.
Programming Options
The Cerebot II provides two in-system
programming connections, J1 and J2.
Connector J1 is the Digilent ISP connector.
This provides for in-system programming using
a Digilent parallel JTAG/SPI cable or a Digilent
USB-JTAG/SPI cable. When connecting the
Digilent JTAG/SPI cables, ensure that the VCC
and GND pin labels from the cable match to
the VCC and GND pins on the Cerebot II.
When using a Digilent programming cable, use
the Digilent AVR Programmer application
available for download from the Digilent web
site (
www.digilentinc.com ) to program the
board.
Connector J2 is a 6-pin (3x2) header for in-
system programming using the Atmel AVRISP
(Atmel P/N ATAVRISP) programmer. When
connecting to the Cerebot II, the red indicator
line on the AVRISP connection plug must be
aligned with the top pins MISO and VCC on J2.
Programming can be accomplished using
several AVR programming applications
including the Digilent AVR Programmer
(AVRP), AVRDUDE from the WinAVR tool set,
and Atmel’s AVR Studio. Programming via
AVR Studio requires use of the Atmel AVRISP
programmer hardware. See the user’s
documentation for each of these applications
for more information on board programming.
Debugging with the Atmel
JTAGICE mkII
Connector J6 on the Cerebot II is provided for
the Atmel JTAGICE mkII (Atmel P/N
ATJTAGICE2) in-circuit emulator for
debugging purposes. The JTAGICE works with
the debugger in Atmel’s AVR Studio product.
The JTAG port on the ATmega64 must be
enabled when using the JTAGICE. The
Cerebot II is shipped with the JTAG port
disabled. This port can be enabled or disabled
using a fuse bit which can be set with any of
the supported in-system programmers
described above.
Two Wire Serial Interface
The Atmel Two Wire Serial Interface (TWI)
provides a medium speed (400K bps)
synchronous serial communications bus. The
TWI interface provides master and slave
operation with up to 127 devices on the bus.
Each device is given a unique address, and
the protocol provides the ability to address
packets to a specific device or to broadcast
packets to all devices on the bus. See the
ATmega64 data sheet for detailed information
on configuring and using the two wire serial
interface.
The Cerebot II provides two ways to connect to
a TWI bus. The TWI signals (SCL and SDA)
are available on the connector JD (pins 7 and
8) or on the TWI daisy chain connector, J3.
Connector J3 provides two positions for
connecting to the TWI signals. By using two-
wire cables (available separately from Digilent)
a daisy chain of multiple Cerebot II boards or
other TWI-capable boards can be created.
The TWI bus is an open-collector bus. Devices
on the bus actively drive the signals low. The
high state on the TWI lines is achieved by pull-