Datasheet

© 2011 Microchip Technology Inc. DS70150E-page 161
dsPIC30F6010A/6015
21.4 Watchdog Timer (WDT)
21.4.1 WATCHDOG TIMER OPERATION
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, which
runs off an on-chip RC oscillator, requiring no external
component. Therefore, the WDT timer will continue to
operate even if the main processor clock (e.g., the
crystal oscillator) fails.
21.4.2 ENABLING AND DISABLING THE
WDT
The Watchdog Timer can be “Enabled” or “Disabled”
only through a Configuration bit (FWDTEN) in the
Configuration register FWDT.
Setting FWDTEN = 1 enables the Watchdog Timer.
The enabling is done when programming the device.
By default, after chip-erase, FWDTEN bit = 1. Any
device programmer capable of programming
dsPIC30F devices allows programming of this and
other Configuration bits.
If enabled, the WDT will increment until it overflows or
“times out”. A WDT time-out will force a device Reset
(except during Sleep). To prevent a WDT time-out, the
user must clear the Watchdog Timer using a CLRWDT
instruction.
If a WDT times out during Sleep, the device will wake-
up. The WDTO bit in the RCON register will be cleared
to indicate a wake-up resulting from a WDT time-out.
Setting FWDTEN = 0 allows user software to enable/
disable the Watchdog Timer via the SWDTEN
(RCON<5>) control bit.
21.5 Power-Saving Modes
There are two power-saving states that can be entered
through the execution of a special instruction, PWRSAV.
These are: Sleep and Idle.
The format of the PWRSAV instruction is as follows:
PWRSAV <parameter>, where ‘parameter’ defines
Idle or Sleep mode.
21.5.1 SLEEP MODE
In Sleep mode, the clock to the CPU and peripherals is
shut down. If an on-chip oscillator is being used, it is
shut down.
The Fail-Safe Clock Monitor is not functional during
Sleep, since there is no clock to monitor. However,
LPRC clock remains active if WDT is operational during
Sleep.
The Brown-out protection circuit, if enabled, will remain
functional during Sleep.
The processor wakes up from Sleep if at least one of
the following conditions has occurred:
• any interrupt that is individually enabled and
meets the required priority level
• any Reset (POR, BOR and MCLR
)
• WDT time-out
On waking up from Sleep mode, the processor will
restart the same clock that was active prior to entry
into Sleep mode. When clock switching is enabled,
bits COSC<2:0> will determine the oscillator source
that will be used on wake-up. If clock switch is
disabled, then there is only one system clock.
If the clock source is an oscillator, the clock to the
device is held off until OST times out (indicating a
stable oscillator). If PLL is used, the system clock is
held off until LOCK = 1 (indicating that the PLL is
stable).
Either way, T POR , T LOCK and T PWRT delays are
applied .
If EC, FRC, LPRC or ERC oscillators are used, then a
delay of T
POR (~ 10 μs) is applied. This is the smallest
delay possible on wake-up from Sleep.
Moreover, if LP oscillator was active during Sleep, and
LP is the oscillator used on wake-up, then the start-up
delay will be equal to T
POR. PWRT delay and OST
timer delay are not applied. In order to have the small-
est possible start-up delay when waking up from Sleep,
one of these faster wake-up options should be selected
before entering Sleep.
Any interrupt that is individually enabled (using the
corresponding IE bit) and meets the prevailing priority
level will be able to wake-up the processor. The proces-
sor will process the interrupt and branch to the ISR. The
Sleep Status bit in RCON register is set upon wake-up
.
All Resets will wake-up the processor from Sleep
mode. Any Reset, other than POR, will set the Sleep
Status bit. In a POR, the Sleep bit is cleared.
If Watchdog Timer is enabled, then the processor will
wake-up from Sleep mode upon WDT time-out. The
Sleep and WDTO Status bits are both set.
Note: If a POR or BOR occurred, the selection of
the oscillator is based on the FOS<2:0>
and FPR<4:0> Configuration bits.
Note: In spite of various delays applied (T POR ,
T
LOCK and T PWRT ), the crystal oscillator
(and PLL) may not be active at the end of
the time-out (e.g., for low-frequency crys-
tals). In such cases, if FSCM is enabled,
then the device will detect this as a clock
failure and process the clock failure trap,
the FRC oscillator will be enabled, and the
user will have to re-enable the crystal oscil-
lator. If FSCM is not enabled, then the
device will simply suspend execution of
code until the clock is stable, and will
remain in Sleep until the oscillator clock has
started.