DSPIC33FJMC202ESS datasheet(122/330 Pages) MICROCHIP

122 / 330 page

dsPIC33FJ32MC202/204 and dsPIC33FJ16MC304

DS70283K-page 122

10.6.3

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

10.6.3.1

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

(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:

Write 0x46 to OSCCON<7:0>.

Write 0x57 to OSCCON<7:0>.

Clear (or set) IOLOCK as a single operation.

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.

10.6.3.2

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.

10.6.3.3

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<IOL1WAY>) 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.

Note:

MPLAB®

C30

provides

built-in

language functions for unlocking the

OSCCON register:

__builtin_write_OSCCONL(value)

__builtin_write_OSCCONH(value)

See MPLAB Help for more information.

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