Datasheet

 2013-2014 Microchip Technology Inc. DS70000689D-page 165
dsPIC33EPXXXGM3XX/6XX/7XX
11.4 Peripheral Pin Select (PPS)
A major challenge in general purpose devices is provid-
ing the largest possible set of peripheral features while
minimizing the conflict of features on I/O pins. The chal-
lenge is even greater on low pin count devices. In an
application where more than one peripheral needs to
be assigned to a single pin, inconvenient work arounds
in application code or a complete redesign may be the
only option.
Peripheral Pin Select configuration provides an
alternative to these choices by enabling peripheral set
selection and their placement on a wide range of I/O
pins. By increasing the pinout options available on a
particular device, users can better tailor the device to
their entire application, rather than trimming the
application to fit the device.
The Peripheral Pin Select configuration feature oper-
ates over a fixed subset of digital I/O pins. Users may
independently map the input and/or output of most dig-
ital peripherals to any one of these I/O pins. Hardware
safeguards are included that prevent accidental or
spurious changes to the peripheral mapping once it has
been established.
11.4.1 AVAILABLE PINS
The number of available pins is dependent on the
particular device and its pin count. Pins that support the
Peripheral Pin Select feature include the designation,
“RPn” or “RPIn”, in their full pin designation, where “n”
is the remappable pin number. “RP” is used to
designate pins that support both remappable input and
output functions, while “RPI” indicates pins that support
remappable input functions only.
11.4.2 AVAILABLE PERIPHERALS
The peripherals managed by the Peripheral Pin Select
are all digital only peripherals. These include general
serial communications (UART and SPI), general pur-
pose timer clock inputs, timer-related peripherals (input
capture and output compare) and interrupt-on-change
inputs.
In comparison, some digital only peripheral modules are
never included in the Peripheral Pin Select feature. This
is because the peripheral’s function requires special I/O
circuitry on a specific port and cannot be easily con-
nected to multiple pins. These modules include I
2
C™
and the PWM. A similar requirement excludes all
modules with analog inputs, such as the A/D Converter.
A key difference between remappable and non-
remappable peripherals is that remappable peripherals
are not associated with a default I/O pin. The peripheral
must always be assigned to a specific I/O pin before it
can be used. In contrast, non-remappable peripherals
are always available on a default pin, assuming that the
peripheral is active and not conflicting with another
peripheral.
When a remappable peripheral is active on a given I/O
pin, it takes priority over all other digital I/O and digital
communication peripherals associated with the pin.
Priority is given regardless of the type of peripheral that
is mapped. Remappable peripherals never take priority
over any analog functions associated with the pin.
11.4.3 CONTROLLING PERIPHERAL PIN
SELECT
Peripheral Pin Select features are controlled through
two sets of SFRs: one to map peripheral inputs and one
to map outputs. Because they are separately con-
trolled, a particular peripheral’s input and output (if the
peripheral has both) can be placed on any selectable
function pin without constraint.
The association of a peripheral to a peripheral-selectable
pin is handled in two different ways, depending on
whether an input or output is being mapped.