T84C5112-RKREV datasheet(22/97 Pages) ATMEL

22 / 97 page

Rev. B - November 10, 2000

Preliminary

T80C5112

8.1.1.2. Power down and OSCC active

In Power Down mode the low speed RC oscillator never stops. If the WDT is active before entering power down,

the T80C5112 will be reseted once and will start executing the program code. The software may then decide to

leave the WDT inactive.

If the high speed RC oscillator is selected at reset, this mode may be used to periodically awake the T80C5112

and check for an external event while keeping the average consumption at a very low level.

There are 2 methods of exiting Power Down mode: by a hardware or watchdog reset or via a level activated

external interrupt which is enabled prior to entering Power Down mode. When Power Down is exited with hardware

or watch dog reset, servicing the WDT should occur as it normally should whenever the T80C5112 is reset. Exiting

Power Down with an interrupt is significantly different. As the WDT and interrupt are asynchronous events, the

WDT may overflow within a few states of exiting of powerdown. To limit the probability of such an event, it is

suggested that the WDT be reseted during the interrupt service routine.

8.1.1.3. Idle mode

In the Idle mode, the oscillator continues to run. To prevent the WDT from resetting the T80C5112 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.

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