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Philips Semiconductors
WATCHDOG TIMER
MOV WFEED1, #0A5H
MOV WFEED2, #05AH
Watchdog
Oscillator
÷32
CLK
Power down operation
The WDT oscillator will continue to run in power down, consuming approximately 50uA, as long as the WDT oscillator is selected
as the clock source for the WDT. Selecting PCLK as the WDT source will result in the WDT oscillator going into power down
with the rest of the device (see section "Watchdog Clock Source" on page 88 ). Power down mode will also prevent PCLK from
running and therefore the watchdog is effectively disabled.
Periodic wakeup from Power down without an external oscillator
Without using an external oscillator source, the power consumption required in order to have a periodic wakeup is determined
by the power consumption of the internal oscillator source used to produce the wakeup.The Real-time clock running from the
internal RC oscillator can be used. The power consumption of this oscillator is approximately 300uA. Instead, if the WDT is used
to generate interrupts the current is reduced to approximately 50uA. Whenever the WDT underflows, the device will wake up.
2003 Dec 8
PRESCALER
control register
PRE2
PRE1
PRE0
Figure 13-4: Watchdog Timer in Timer Mode (WDTE = 0)
WDL (C1H)
8-Bit Down
Counter
WDRUN
WDTOF
90
User's Manual - Preliminary -
P89LPC920/921/922
Interrupt
SHADOW
REGISTER FOR
WDCON
WDCLK
WDCON(A7H)
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