DSPIC33EP128GS708 datasheet(137/484 Pages) MICROCHIP

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DS70005258C-page 137

dsPIC33EPXXXGS70X/80X FAMILY

11.6

Peripheral Pin Select (PPS)

A major challenge in general purpose devices is

providing the largest possible set of peripheral features,

while minimizing the conflict of features on I/O pins.

The challenge 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 alter-

native to these choices by enabling peripheral set

selection and placement on a wide range of I/O pins.

By increasing the pinout options available on a particu-

lar 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

operates over a fixed subset of digital I/O pins. Users

may independently map the input and/or output of most

digital peripherals to any one of these I/O pins. Hard-

ware safeguards are included that prevent accidental

or spurious changes to the peripheral mapping once it

has been established.

11.6.1

AVAILABLE PINS

The number of available pins is dependent on the par-

ticular device and its pin count. Pins that support the

Peripheral Pin Select feature include the label, “RPn”,

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.

11.6.2

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 connected to multiple pins. One example

includes I2C modules. A similar requirement excludes

all modules with analog inputs, such as the ADC

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/Os 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.

11.6.3

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.

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