DSPIC33FJ32GP302THSLASHML datasheet(164/403 Pages) MICROCHIP

164 / 403 page

dsPIC33FJ32GP302/304, dsPIC33FJ64GPX02/X04, AND dsPIC33FJ128GPX02/X04

DS70292D-page 164

Preliminary

 2009 Microchip Technology Inc.

11.6.3

CONTROLLING CONFIGURATION

CHANGES

Because peripheral remapping can be changed during

run time, some restrictions on peripheral remapping

are

needed

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

11.6.3.1

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 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;

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.

11.6.3.2

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 is

triggered.

11.6.3.3

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 does 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 C language

functions for unlocking the OSCCON

__builtin_write_OSCCONL(value)

__builtin_write_OSCCONH(value)

See MPLAB Help for more information.

DSPIC33FJ32GP302TH/ML Datasheet(PDF) 164 Page - Microchip Technology

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