Errata ATmega48
Rev A
The revision letter in this section refers to the revision of the ATmega48 device.
• Wrong values read after Erase Only operation
• Watchdog Timer Interrupt disabled
• Start-up time with Crystal Oscillator is higher than expected
• High Power Consumption in Power-down with External Clock
• Asynchronous Oscillator does not stop in Power-down
1. Wrong values read after Erase Only operation
At supply voltages below 2.7 V, an EEPROM location that is erased by the Erase
Only operation may read as programmed (0x00).
Problem Fix/Workaround
If it is necessary to read an EEPROM location after Erase Only, use an Atomic Write
operation with 0xFF as data in order to erase a location. In any case, the Write Only
operation can be used as intended. Thus no special considerations are needed as
long as the erased location is not read before it is programmed.
2. Watchdog Timer Interrupt disabled
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.
3. Start-up time with Crystal Oscillator is higher than expected
The clock counting part of the start-up time is about 2 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 32 kHz clock crystal.
Problem fix / Workaround
No known workaround.
4. High Power Consumption in Power-down with External Clock
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.
5. Asynchronous Oscillator does not stop 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.
338
ATmega48/88/168
2545D–AVR–07/04
ATMEL [ ATMEL ]
