Digilent MX3cK - Manual (Page 7)

Cerebot MX3cK Reference Manual
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protects the I/O block from damage due to
electro-static discharge.
Although ESD protection is provided between
the connector pins and the microcontroller
pins, ESD safe handling procedures should be
followed when handling the circuit board. The
pins on the microcontroller and other circuits
on the board are exposed and can be
damaged through ESD when handling the
board.
Digilent Pmod peripheral modules can either
be plugged directly into the connectors on the
Cerebot MX3cK or attached via cables.
Digilent has a variety of Pmod interconnect
cables available.
See the Pinout Tables in Appendices B–D
below for more information about connecting
peripheral modules and other devices to the
Cerebot MX3cK. These tables indicate the
mapping between pins on the PIC32MX320
microcontroller and the pins on the various
connectors.
The PIC32 microcontroller can source or sink a
maximum of 18mA on all digital I/O pins.
However, to keep the output voltage within the
specified input/output voltage range (V
OL
0.4V,
V
OH
2.4V) the pin current must be restricted to
+7/-12mA. The maximum current that can be
sourced or sunk across all I/O pins
simultaneously is +/-200mA. The maximum
voltage that can be applied to any digital I/O
pin is 5.5V. For more detailed specifications,
refer to the PIC32MX3XX/4XX Data Sheet.
Digital Inputs and Outputs
The Cerebot MX3cK board provides access to
40 of the I/O pins from the PIC32
microcontroller via the Pmod connectors. Two
additional I/O pins can be accessed via the I
2 C
connector, J2. Any of the pins on the Pmod or
I
2 C connectors can be individually accessed for
digital input or output. Note that when the I 2 C
signals on J2 are being used for I 2 C
communications, they are not available for
general purpose I/O.
On PIC32 microcontrollers, the input/output
pins are grouped into I/O Ports and are
accessed via peripheral registers in the
microcontroller. There are seven I/O Ports
numbered A–G and each is 16 bits wide.
Depending on the particular PIC32
microcontroller, some of the I/O Ports are not
present, and not all 16 bits are present in all
I/O Ports.
Each I/O Port has four control registers: TRIS,
LAT, PORT, and ODC. The registers for I/O
Port A are named TRISA, LATA, PORTA and
ODCA. The registers for the other I/O Ports are
named similarly.
The TRIS register is used to set the pin
direction. Setting a TRIS bit to 0 makes the pin
an output. Setting the TRIS bit to 1 makes the
pin an input.
The LAT register is used to write to the I/O
Port. Writing to the LAT register sets any pins
configured as outputs. Reading from the LAT
register returns the last value written.
The PORT register is used to read from the I/O
Port. Reading from the PORT register returns
the current state of all of the pins in the I/O
Port. Writing to the PORT register is equivalent
to writing to the LAT register.
PIC32 microcontrollers allow any pin set as an
output to be configured as either a normal
totem-pole output or as an open-drain output.
The ODC register is used to control the output
type. Setting an ODC bit to 0 makes the pin a
normal output and setting it to 1 makes the pin
a open drain output.
Refer to the PIC32MX3XX/4XX Family Data
Sheet, and the PIC32 Family Reference
Manual, Section 12, IO Ports, for more detailed
information about the operation of the I/O Ports
in the microcontroller.
The chipKIT MPIDE system uses logical pin
numbers to identify digital I/O pins on the