Datasheet

© 2005 Microchip Technology Inc. DS70043F-page 21
dsPIC30F
7.6 Watchdog Timer (WDT)
The primary function of the Watchdog Timer (WDT) is
to reset the processor in the event of a software
malfunction. The WDT is a free running timer that runs
off an on-chip RC oscillator, requiring no external
component. The WDT Timer continues to operate even
if the main processor clock (e.g., the crystal oscillator)
fails.
The Watchdog Timer can be “Enabled” or “Disabled”
either through a Configuration bit (FWDTEN) in the
Configuration register or through an SFR bit
(SWDTEN).
Any device programmer capable of programming
dsPIC devices (such as Microchip’s PRO MATE
®
II
programmer) allows programming of this and other
Configuration bits to the desired state. If enabled, the
WDT increments until it overflows or “times out”. A
WDT time-out forces a device Reset (except during
Sleep).
7.7 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.
7.8 Reset System
The Reset system combines all Reset sources and
controls the device Master Reset signal.
Device Reset sources include:
• POR: Power-on Reset
•SWR: RESET instruction
• EXTR: MCLR
Reset
• WDTR: Watchdog Timer Time-out Reset
• BOR: Brown-out Reset
• TRAPR: Trap Conflict Reset
• IOPUWR: Attempted execution of an Illegal
Opcode, or Indirect Addressing using an
Uninitialized W Register