Digilent MX4cK - Manual (Page 9)

Cerebot MX4cK Reference Manual
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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 Family Data
Sheet.
Digital Inputs and Outputs
The Cerebot MX4cK board provides access to
72 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, J6. 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 J6 are being used for I 2 C
communications, they are not available for
general purpose I/O. Note that the signals on
I
2
C connector J2 are shared with pins 1 & 2 of
Pmod connector JF.
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
connectors. These pin numbers start with pin 0
and are numbered up consecutively.
On the Cerebot MX4cK, pin numbers 0–71 are
used to access the pins on the Pmod
connectors and pin numbers 72 and 73 are
used for the two signal pins on the I
2 C
connector, J6. The pin numbers are assigned
so that connector JA pin 1 (JA-01) is digital pin
0, JA pin 2 (JA-02) is digital pin 1, and so on.
Pins 0-7 are on connector JA, pins 8-15 on JB,
pins 16-23 on JC, pins 24-31 and so on. Refer
to the tables in Appendix C for detailed
information about the pin mapping between
Pmod connector, logical pin number, and
PIC32 microcontroller pin number and pin
function.