ATMEGA48V_11 ATMEL [ATMEL Corporation], ATMEGA48V_11 Datasheet - Page 359

• Manufacturer Part Number: ATMEGA48V_11
• Description: 8-bit Atmel Microcontroller with 4/8/16K Bytes In-System Programmable Flash
• Manufacturer: ATMEL [ATMEL Corporation]

2545T–AVR–05/11
3. Watchdog timer interrupt disabled
4. Start-up time with crystal oscillator is higher than expected
5. High power consumption in power-down with external clock
6. Asynchronous oscillator does not stop in power-down
7. Interrupts may be lost when writing the timer registers in the asynchronous timer
If the watchdog timer interrupt flag is not cleared before a new timeout occurs, the watchdog
will be disabled, and the interrupt flag will automatically be cleared. This is only applicable in
interrupt only mode. If the Watchdog is configured to reset the device in the watchdog time-
out following an interrupt, the device works correctly.
Problem fix/workaround
Make sure there is enough time to always service the first timeout event before a new
watchdog timeout occurs. This is done by selecting a long enough time-out period.
The clock counting part of the start-up time is about two times higher than expected for all
start-up periods when running on an external Crystal. This applies only when waking up by
reset. Wake-up from power down is not affected. For most settings, the clock counting parts
is a small fraction of the overall start-up time, and thus, the problem can be ignored. The
exception is when using a very low frequency crystal like for instance a 32kHz clock crystal.
Problem fix/workaround
No known workaround.
The power consumption in power down with an active external clock is about 10 times
higher than when using internal RC or external oscillators.
Problem fix/workaround
Stop the external clock when the device is in power down.
The Asynchronous oscillator does not stop when entering power down mode. This leads to
higher power consumption than expected.
Problem fix/workaround
Manually disable the asynchronous timer before entering power down.
The interrupt will be lost if a timer register that is synchronous timer clock is written when the
asynchronous Timer/Counter register (TCNTx) is 0x00.
Problem fix/workaround
Always check that the asynchronous Timer/Counter register neither have the value 0xFF nor
0x00 before writing to the asynchronous Timer Control Register (TCCRx), asynchronous
Timer Counter Register (TCNTx), or asynchronous Output Compare Register (OCRx).
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