DSPIC33FJ16GS502-I Datasheet, PDF (162/346 Pages) Microchip Technology – High-Performance, 16-bit Digital Signal Controllers

dsPIC33FJ06GS101/X02 and dsPIC33FJ16GSX02/X04
10.4.2.3 Virtual Pins
dsPIC33FJ06GS101/X02
and
dsPIC33FJ16GSX02/X04 devices support four virtual
RPn pins (RP32, RP33, RP34 and RP35), which are
identical in functionality to all other RPn pins, with the
exception of pinouts. These four pins are internal to the
devices and are not connected to a physical device pin.
These pins provide a simple way for inter-peripheral
connection without utilizing a physical pin. For example,
the output of the analog comparator can be connected to
RP32 and the PWM Fault input can be configured for
RP32 as well. This configuration allows the analog
comparator to trigger PWM Faults without the use of an
actual physical pin on the device.
10.4.3 CONTROLLING CONFIGURATION
CHANGES
Because peripheral remapping can be changed during
run time, some restrictions on peripheral remapping
are needed to prevent accidental configuration
changes. dsPIC33F devices include three features to
prevent alterations to the peripheral map:
• Control register lock sequence
• Continuous state monitoring
• Configuration bit pin select lock
10.4.3.1 Control Register Lock
Under normal operation, writes to the RPINRx and
RPORx registers are not allowed. Attempted writes
appear to execute normally, but the contents of the
registers 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; clearing IOLOCK allows writes.
To set or clear IOLOCK, a specific command sequence
must be executed:
1. Write 0x46 to OSCCON<7:0>.
2. Write 0x57 to OSCCON<7:0>.
3. Clear (or set) IOLOCK as a single operation.
Note:
MPLAB^® C30 provides built-in C language
functions for unlocking the OSCCON
register:
__builtin_write_OSCCONL(value)
__builtin_write_OSCCONH(value)
See MPLAB C30 Help files for more
information.
Unlike the similar sequence with the oscillator’s LOCK
bit, IOLOCK remains in one state until changed. This
allows all of 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.
10.4.3.2 Continuous State Monitoring
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.
10.4.3.3 Configuration Bit Pin Select Lock
As an additional level of safety, the device can be
configured to prevent more than one write session to
the RPINRx and RPORx registers. The IOL1WAY
(FOSC<5>) Configuration bit blocks the IOLOCK bit
from being cleared after it has been set once. If
IOLOCK remains set, the register unlock procedure will
not execute and the Peripheral Pin Select Control
registers cannot be written to. The only way to clear the
bit and re-enable peripheral remapping is to perform a
device Reset.
In the default (unprogrammed) state, IOL1WAY is set,
restricting 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.
DS70318D-page 160
Preliminary
© 2009 Microchip Technology Inc.