33FJ128GP708 datasheet(23/90 Pages) MICROCHIP

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Preliminary

DS70155C-page 21

dsPIC33F

6.5

Fail-Safe Clock Monitor (FSCM)

The Fail-Safe Clock Monitor (FSCM) allows the device

to continue to operate even in the event of an oscillator

failure. The FSCM function is enabled by programming.

If the FSCM function is enabled, the LPRC internal

oscillator runs at all times (except during Sleep mode)

and is not subject to control by the Watchdog Timer.

In the event of an oscillator failure, the FSCM

generates a clock failure trap event and switches the

system clock over to the FRC oscillator. The application

program then can either attempt to restart the oscillator,

or execute a controlled shutdown. The trap can be

treated as a warm Reset by simply loading the Reset

address into the oscillator fail trap vector.

6.6

Reset System

The Reset system combines all Reset sources and

controls the device Master Reset signal.

Device Reset sources include:

• POR: Power-on Reset

• BOR: Brown-out Reset

•SWR: RESET Instruction

• EXTR: MCLR Reset

• WDTR: Watchdog Timer Time-out Reset

• TRAPR: Trap Conflict

• IOPUWR: Attempted execution of an Illegal

Opcode, or Indirect Addressing, using an

Uninitialized W register

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