PIC24HJ12GP201 Datasheet, PDF (93/234 Pages) Microchip Technology – High-Performance, 16-Bit Microcontrollers

PIC24HJ12GP201/202
9.4 Peripheral Pin Select
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 must be assigned to a single pin,
inconvenient workarounds in application code or a
complete redesign may be the only option.
Peripheral pin select configuration enables peripheral
set selection and placement on a wide range of I/O
pins. By increasing the pinout options available on a
particular device, programmers can better tailor the
microcontroller 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. Pro-
grammers can independently map the input and/or out-
put of most digital peripherals to any one of these I/O
pins. Peripheral pin select is performed in software,
and generally does not require the device to be
reprogrammed. Hardware safeguards are included that
prevent accidental or spurious changes to the
peripheral mapping, once it has been established.
9.4.1 AVAILABLE PINS
The peripheral pin select feature is used with a range
of up to 16 pins. The number of available pins depends
on the particular device and its pin count. Pins that
support the peripheral pin select feature include the
designation “RPn” in their full pin designation, where
“RP” designates a remappable peripheral and “n” is the
remappable pin number.
9.4.2 AVAILABLE PERIPHERALS
The peripherals managed by the peripheral pin select
feature are all digital-only peripherals. These include:
• General serial communications (UART and SPI)
• General purpose timer clock inputs
• Timer-related peripherals (input capture and
output compare)
• 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 spe-
cial I/O circuitry on a specific port and cannot be easily
connected to multiple pins. These modules include I²C.
A similar requirement excludes all modules with analog
inputs, such as the Analog-to-Digital Converter (ADC).
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 avail-
able on a default pin, assuming that the peripheral is
active and not conflicting with another peripheral.
9.4.2.1
Peripheral Pin Select Function
Priority
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.
9.4.3
CONTROLLING PERIPHERAL PIN
SELECT
Peripheral pin select features are controlled through
two sets of special function registers: one to map
peripheral inputs, and one to map outputs. Because
they are separately controlled, 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.
9.4.3.1 Input Mapping
The inputs of the peripheral pin select options are
mapped on the basis of the peripheral. A control
register associated with a peripheral dictates the pin it
will be mapped to. The RPINRx registers are used to
configure peripheral input mapping (see Register 9-1
through Register 9-9). Each register contains sets of
5-bit fields, with each set associated with one of the
remappable peripherals. Programming a given
peripheral’s bit field with an appropriate 5-bit value
maps the RPn pin with that value to that peripheral.
For any given device, the valid range of values for any
bit field corresponds to the maximum number of
peripheral pin selections supported by the device.
Figure 9-2 Illustrates remappable pin selection for
U1RX input.
© 2007 Microchip Technology Inc.
Preliminary
DS70282B-page 91