Digilent Cerebot II Reference Manual - Page 5

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Cerebot II Reference Manual

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
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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-
up resistors when no device is driving the lines
low. One device on the TWI bus must provide
the pull-up resistors. The Cerebot II board
provides pull-up resistors that can be enabled
or disabled via jumper blocks on the 'pull-up'
positions on J3. The pull-ups are enabled by
installing jumper blocks on J3 and are disabled
by removing the jumper blocks. The shorting
blocks are placed so that they line up with the
SCL and SDA labels on the board. Only one
device on the bus should have the pull-ups
enabled.
Digilent, Inc.
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