Digilent MX7cK - Manual (Page 8)

Cerebot MX7cK Reference Manual
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+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. The maximum voltage that can be
applied to any analog input capable pin is
3.6V. For more detailed specifications, refer to
the PIC32MX5XX/6XX/7XX Family Data
Sheet.
Digital Inputs and Outputs
The Cerebot MX7cK board provides access to
48 of the I/O pins from the PIC32MX795
microcontroller via the Pmod connectors. Four
additional I/O pins can be accessed via the I
2 C
connectors, J7 and J8. 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 J7 or J8 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 associated 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
an open drain output.
Refer to the PIC32MX5XX/6XX/7XX 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.
Pmod connector JF, pins 8, 9, and 10 are
connected to the signals TCK/RA1, TDI/RA4,
and TDO/RA5 respectively. These
microcontroller pins are shared between
general purpose I/O functions and use by the
JTAG controller. The JTAG controller is
enabled on reset, so these pins are not
available for general purpose I/O until the
JTAG controller is disabled. The following
statement can be used to disable the JTAG
controller:
DDPCONbits.JTAGEN = 0;
The JTAG controller is disabled by the startup
initialization code in the MPIDE runtime. It is
not necessary to disable the JTAG controller
when using the board with MPIDE.
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 MX7cK, pin numbers 0-47 are
used to access the pins on the Pmod
connectors and pin numbers 55-58 are used
for the signal pins on the I
2
C connectors, J7
and J8. 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.