18.4 WDT during Power-Down and Idle
In Power-down mode the oscillator stops, which means the WDT also stops. While in Power-down mode the user
does not need to service the WDT. There are 3 methods of exiting Power-down mode: by a hardware reset, via
an external interrupt (/INT0~/INT3) or Keypad interrupt which is enabled prior to entering Power-down mode.
When Power-down is exited with hardware reset, servicing the WDT should occur as it normally should whenever
the device is reset. Exiting Power-down with an external interrupt or Keypad interrupt is significantly different.
When the interrupt is serviced just after exiting the power-down, to prevent the WDT from resetting the device, it
is suggested that the WDT counter should be cleared during the interrupt service routine.
Of course, to ensure that the WDT does not overflow within a little time after exiting of power-down, it is better to
clear the WDT counter just before entering power-down.
In the Idle mode, the oscillator continues to run. The user may either set the WIDL bit to have WDT keep working
or clear the WIDL bit to have WDT stop while the MCU is in the Idle mode. For the former case, to prevent the
WDT from overflowing while in Idle mode, the user should always set up a timer that will periodically exit Idle,
service the WDT, and re-enter Idle mode.
18.5 WDT Initialized by Hardware Option
Besides being initialized by software, the WDTCR register can also be automatically initialized at power-up by the
hardware options HWENW, HWWIDL and HWPS[2:0], which should be programmed by a universal Writer or
Programmer, as described below. (Refer to Section 25: MCU’s Hardware Option.)
If HWENW is programmed to “enabled”, then hardware will automatically do the following initialization for the
WDTCR register at power-up:
(1) set ENW bit,
(2) load HWWIDL into WIDL bit, and
(3) load HWPS[2:0] into PS[2:0] bits.
MEGAWIN
MPC82G516A Data Sheet
88
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