DSPIC30F5011-20I Datasheet, PDF (152/224 Pages) Microchip Technology – dsPIC30F5011/5013 Data Sheet

dsPIC30F5011/5013
20.4 Watchdog Timer (WDT)
20.4.1 WATCHDOG TIMER OPERATION
The primary function of the Watchdog Timer (WDT) is
to reset the processor in the event of a software mal-
function. The WDT is a free-running timer which runs
off an on-chip RC oscillator, requiring no external com-
ponent. Therefore, the WDT timer will continue to oper-
ate even if the main processor clock (e.g., the crystal
oscillator) fails.
20.4.2 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.
20.5 Low-Voltage Detect
The Low-Voltage Detect (LVD) module is used to
detect when the VDD of the device drops below a
threshold value, VLVD, which is determined by the
LVDL<3:0> bits (RCON<11:8>) and is thus user pro-
grammable. The internal voltage reference circuitry
requires a nominal amount of time to stabilize, and the
BGST bit (RCON<13>) indicates when the voltage ref-
erence has stabilized.
In some devices, the LVD threshold voltage may be
applied externally on the LVDIN pin.
The LVD module is enabled by setting the LVDEN bit
(RCON<12>).
20.6 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.
20.6.1 SLEEP MODE
In Sleep mode, the clock to the CPU and peripherals is
shutdown. If an on-chip oscillator is being used, it is
shutdown.
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 and the Low-Voltage
Detect 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<1:0> will determine the oscillator source that
will be used on wake-up. If clock switch is disabled,
then there is only one system clock.
Note:
If a POR or BOR occurred, the selection of
the oscillator is based on the FOS<1:0>
and FPR<3:0> Configuration bits.
If the clock source is an oscillator, the clock to the
device will be 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). In either case, TPOR, TLOCK and TPWRT delays
are applied.
If EC, FRC, LPRC or EXTRC oscillators are used, then
a delay of TPOR (~ 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 TPOR. 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.
DS70116F-page 150
© 2006 Microchip Technology Inc.