![](http://datasheet.mmic.net.cn/100000/IF180C52TXXX-20R_datasheet_3493957/IF180C52TXXX-20R_816.png)
816
32099I–01/2012
AT32UC3L016/32/64
- Disable RC32K by writing a zero to SCIF.RC32KCR.EN, and wait for this bit to be read as
zero.
35.2.5
AST
1.
Reset may set status bits in the AST
If a reset occurs and the AST is enabled, the SR.ALARM0, SR.PER0, and SR.OVF bits may
be set.
Fix/Workaround
If the part is reset and the AST is used, clear all bits in the Status Register before entering
sleep mode.
2.
AST wake signal is released one AST clock cycle after the BUSY bit is cleared
After writing to the Status Clear Register (SCR) the wake signal is released one AST clock
cycle after the BUSY bit in the Status Register (SR.BUSY) is cleared. If entering sleep mode
directly after the BUSY bit is cleared the part will wake up immediately.
Fix/Workaround
Read the Wake Enable Register (WER) and write this value back to the same register. Wait
for BUSY to clear before entering sleep mode.
35.2.6
WDT
1.
Clearing the Watchdog Timer (WDT) counter in second half of timeout period will
issue a Watchdog reset
If the WDT counter is cleared in the second half of the timeout period, the WDT will immedi-
ately issue a Watchdog reset.
Fix/Workaround
Use twice as long timeout period as needed and clear the WDT counter within the first half
of the timeout period. If the WDT counter is cleared after the first half of the timeout period,
you will get a Watchdog reset immediately. If the WDT counter is not cleared at all, the time
before the reset will be twice as long as needed.
2.
WDT Control Register does not have synchronization feedback
When writing to the Timeout Prescale Select (PSEL), Time Ban Prescale Select (TBAN),
Enable (EN), or WDT Mode (MODE) fieldss of the WDT Control Register (CTRL), a synchro-
nizer is started to propagate the values to the WDT clcok domain. This synchronization
takes a finite amount of time, but only the status of the synchronization of the EN bit is
reflected back to the user. Writing to the synchronized fields during synchronization can lead
to undefined behavior.
Fix/Workaround
-When writing to the affected fields, the user must ensure a wait corresponding to 2 clock
cycles of both the WDT peripheral bus clock and the selected WDT clock source.
-When doing writes that changes the EN bit, the EN bit can be read back until it reflects the
written value.
35.2.7
GPIO
1.
Clearing GPIO interrupt may fail
Writing a one to the GPIO.IFRC register to clear an interrupt will be ignored if interrupt is
enabled for the corresponding port.
Fix/Workaround
Disable the interrupt, clear it by writing a one to GPIO.IFRC, then enable the interrupt.