Cerebot MX7cK Reference Manual
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page 17 of 34
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DSPI2
object class is used to access SPI4,
Pmod connector JF.
I
2
C™ Interface
The Inter-Integrated Circuit (I
2
C
TM
) Interface
provides a medium speed (100K or 400K bps)
synchronous serial communications bus. The
I
2
C 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 PIC32MX5XX/6XX/7XX
Family Data Sheet and the PIC32 Family
Reference Manual, Section 24, Inter-Integrated
Circuit, for detailed information on configuring
and using the I
2
C interface.
The PIC32MX795 microcontroller provides for
up to five independent I
2
C interfaces. The
Cerebot MX7cK is designed to provide
dedicated access to two of these interfaces
I2C1 and I2C2 via I
2
C daisy chain connectors
J7 and J8. Connector J7 provides access to
I2C1 while connector J8 provides access to
I2C2.
In addition to I2C1 and I2C2, two other I
2
C
interfaces, I2C3 and I2C5 can be accessed via
pins on Pmod connectors. I2C3 can be
accessed via Pmod connector JE, pins JE-02
(SCL3) and JE-03 (SDA3). I2C5 can be
accessed via Pmod connector JF, pins JF-02
(SCL5) and JF-03 (SDA5)
The I
2
C daisy chain connectors, J7 and J8,
each provide two positions for connecting to
the I
2
C signals, power and ground. By using
two-wire or four-wire MTE cables (available
separately from Digilent) a daisy chain of
multiple Cerebot MX7cK boards or other I
2
C-
capable boards can be created.
The I
2
C bus is an open-collector bus. Devices
on the bus actively drive the signals low. The
high state on the I
2
C signals is achieved by
pull-up resistors when no device is driving the
lines low. One device on the I
2
C bus must
provide the pull-up resistors.
On the Cerebot MX7cK, I2C2, connector J8,
has permanently connected, 2.2K ohm, pull-up
resistors. I2C1, connector J7, provides
selectable pull-ups that can be enabled or
disabled via jumper blocks JP3 and JP4. The
pull-ups are enabled by installing shorting
blocks on JP3 and JP4. They are disabled by
removing the shorting blocks. Only one device
on the bus should have the pull-ups enabled.
If the I
2
C interfaces on Pmod connectors JE or
JF are being used, external pull-up resistors
must be provided. These resistors can be in
the range 1K ohm to 10K ohm, and should be
connected to pull the pins to 3.3V.
The pull-ups on I2C1 on the Cerebot MX7cK
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 I
2
C signals and provides the
ability to drive longer cable runs reliably than
would be the case with simple pull-up resistors.
Jumper Settings for I
2
C Pull-Up Resistors
When using the Cerebot MX7cK with the
MPIDE and the chipKIT system, the I
2
C
interfaces are accessed using the standard
chipKIT Wire library, or the Digilent DTWI
library.
