Digilent Cerebot 32MX7 Reference Manual - Page 7
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Cerebot 32MX7 Reference Manual
enable/disable the termination resistor for the
CAN1 network connector, and JP7 is used to
enable/disable the termination resistor for
CAN2. Install a shorting block on the jumper
pins to enable the termination resistor, or
remove the shorting block to disable the
termination resistor.
I2C Interfaces
The Inter-Integrated Circuit (I2C
provides a medium speed (100K or 400K bps)
synchronous serial communications bus. The
I2C interface provides master and slave
operation using either 7 bit or 10 bit device
addressing. 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.
Refer to the Microchip PIC32MX7XX Data
Sheet and the PIC32 Family Reference
Manual for detailed information on configuring
and using the I2C interface.
The PIC32MX795 microcontroller provides for
up to five independent I2C interfaces. The
Cerebot 32MX7 is designed to provide
dedicated access to two of these interfaces
I2C #1 and I2C #2. There are two sets of
connectors on the board for access to the two
I2C ports. Connector J8 provides access to
I2C port #1 while connector J7 provides
access to I2C port #2.
Each I2C connector provides two positions for
connecting to the I2C signals, power and
ground. By using two-wire or four-wire MTE
cables (available separately from Digilent) a
daisy chain of multiple Cerebot 32MX7 boards
or other I2C-capable boards can be created.
The I2C bus is an open-collector bus. Devices
on the bus actively drive the signals low. The
high state on the I2C signals is achieved by
pull-up resistors when no device is driving the
lines low. One device on the I2C bus must
provide the pull-up resistors. I2C bus #1 has
permanently connected pull-up resistors. I2C
bus #2 provides selectable pull-up resistors
that can be enabled or disabled via jumper
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TM
) Interface
blocks on the „pull-up‟ positions on connector
J2. The pull-ups are enabled by installing
shorting blocks and are disabled by removing
the shorting 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.
The I2C pull-up resistors on I2C bus #2 on the
Cerebot 32MX7 board are actually
implemented using current mirrors rather than
simple resistors. These current mirrors source
approximately 1.7mA. The use of current
mirrors provides faster rise times on the I2C
signals and provides the ability to drive longer
cable runs reliably than would be the case with
simple pull-up resistors.
Pull-ups
Enabled
Jumper Settings for I2C Pull-Up Resistors
On-Board I2C Peripheral Device
The Cerebot 32MX7 provides one on-board
I2C peripheral device, a Microchip 24LC256
serial EEPROM. This device is connected to
I2C bus #1. The 24LC256 is a 256Kbit
(32Kbyte) serial EEPROM device to provide
non-volatile memory storage. The device
address for the 24LC256 is 1010000 (0x50).
Refer to the Microchip data sheet for detailed
information on the operation of this device.
Pmod Connectors
The Cerebot 32MX7 has six Pmod connectors
for connecting Digilent Pmod peripheral
modules. Digilent Pmods are a line of small
peripheral modules that provide various kind of
I/O interfaces. The Pmod line includes such
Pull-ups
Disabled
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