pic24hj16gp304 Microchip Technology Inc., pic24hj16gp304 Datasheet - Page 100

• Manufacturer Part Number: pic24hj16gp304
• Description: High-performance, 16-bit Microcontrollers
• Manufacturer: Microchip Technology Inc.

PIC24HJ32GP202/204 and PIC24HJ16GP304
9.4.3.3
The control schema of peripheral select pins is not lim-
ited to a small range of fixed peripheral configurations.
There are no mutual or hardware-enforced lockouts
between any of the peripheral mapping SFRs. Literally
any combination of peripheral mappings across any or
all of the RPn pins is possible. This includes both
many-to-one and one-to-many mappings of peripheral
inputs and outputs to pins.
While such mappings may be technically possible from
a configuration point of view, they may not be support-
able electrically.
9.4.4
Because peripheral remapping can be changed during
run time, some restrictions on peripheral remapping
are needed to prevent accidental configuration
changes. PIC24H devices include three features to
prevent alterations to the peripheral map:
• Control register lock sequence
• Continuous state monitoring
• Configuration bit pin select lock
9.4.4.1
Under normal operation, writes to the RPINRx and
RPORx registers are not allowed. Attempted writes
appear to execute normally, but the contents of the reg-
isters remain unchanged. To change these registers,
they must be unlocked in hardware. The register lock is
controlled by the IOLOCK bit (OSCCON<6>). Setting
IOLOCK prevents writes to the control registers; clear-
ing IOLOCK allows writes.
To set or clear IOLOCK, a specific command sequence
must be executed:
1.
2.
3.
Unlike the similar sequence with the oscillator’s LOCK
bit, IOLOCK remains in one state until changed. This
allows all the peripheral pin selects to be configured
with a single unlock sequence followed by an update to
all control registers, then locked with a second lock
sequence.
DS70289A-page 98
Note:
Write 46h to OSCCON<7:0>.
Write 57h to OSCCON<7:0>.
Clear (or set) IOLOCK as a single operation.
CONTROLLING CONFIGURATION
CHANGES
MPLAB
functions for unlocking the OSCCON
register:
See MPLAB Help for more information.
Mapping
Control Register Lock
__builtin_write_OSCCONL(value)
__builtin_write_OSCCONH(value)
®
C30 provides built-in C language
Preliminary
9.4.4.2
In addition to being protected from direct writes, the
contents of the RPINRx and RPORx registers are
constantly monitored in hardware by shadow registers.
If an unexpected change in any of the registers occurs
(such as cell disturbances caused by ESD or other
external events), a configuration mismatch Reset will
be triggered.
9.4.4.3
As an additional level of safety, the device can be con-
figured to prevent more than one write session to the
RPINRx and RPORx registers. The IOL1WAY
(FOSC<IOL1WAY>) configuration bit blocks the
IOLOCK bit from being cleared after it has been set
once.
In the default (unprogrammed) state, IOL1WAY is set
restricting the users to one write session. Programming
IOL1WAY allows user applications unlimited access
(with the proper use of the unlock sequence) to the
peripheral pin select registers.
9.4.5
The ability to control peripheral pin selection introduces
several considerations into application design, includ-
ing several common peripherals that are only available
as remappable peripherals.
9.4.5.1
The peripheral pin selects are not available on default
pins in the device’s default (Reset) state. More specifi-
cally, since all RPINRx and RPORx registers reset to
0000h, this means all peripheral pin select inputs are
tied to RP0, while all peripheral pin select outputs are
disconnected. This means that before any other appli-
cation code is executed, the user application must ini-
tialize
configuration.
Since the IOLOCK bit resets in the unlocked state, it is
not necessary to execute the unlock sequence after the
device has come out of Reset. For the sake of applica-
tion safety, however, it is always a good idea to set
IOLOCK and lock the configuration after writing to the
control registers.
Because the unlock sequence is timing-critical, it must
be executed as an assembly-language routine, in the
same
configuration. If the bulk of the application is written in
C or another high-level language, the unlock sequence
should be performed by writing inline assembly.
the
manner
CONSIDERATIONS FOR
PERIPHERAL PIN SELECTION
Continuous State Monitoring
Configuration Bit Pin Select Lock
Configuration
device
as
with
changes
© 2007 Microchip Technology Inc.
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