ATMEGA8_06 Datasheet, PDF (17/23 Pages) ATMEL Corporation – 8-bit AVR with 8K Bytes In-System Programmable Flash

Erratas
ATmega8
Rev. D to I
2486QS–AVR–10/06
ATmega8(L)
The revision letter in this section refers to the revision of the ATmega8 device.
• First Analog Comparator conversion may be delayed
• Interrupts may be lost when writing the timer registers in the asynchronous timer
• Signature may be Erased in Serial Programming Mode
• CKOPT Does not Enable Internal Capacitors on XTALn/TOSCn Pins when 32 KHz
Oscillator is Used to Clock the Asynchronous Timer/Counter2
1. First Analog Comparator conversion may be delayed
If the device is powered by a slow rising V_CC, the first Analog Comparator conver-
sion will take longer than expected on some devices.
Problem Fix/Workaround
When the device has been powered or reset, disable then enable theAnalog Com-
parator before the first conversion.
2. Interrupts may be lost when writing the timer registers in the asynchronous
timer
If one of the timer registers which is synchronized to the asynchronous timer2 clock
is written in the cycle before a overflow interrupt occurs, the interrupt may be lost.
Problem Fix/Workaround
Always check that the Timer2 Timer/Counter register, TCNT2, does not have the
value 0xFF before writing the Timer2 Control Register, TCCR2, or Output Compare
Register, OCR2
3. Signature may be Erased in Serial Programming Mode
If the signature bytes are read before a chiperase command is completed, the sig-
nature may be erased causing the device ID and calibration bytes to disappear. This
is critical, especially, if the part is running on internal RC oscillator.
Problem Fix/Workaround:
Ensure that the chiperase command has exceeded before applying the next
command.
4. CKOPT Does not Enable Internal Capacitors on XTALn/TOSCn Pins when
32 KHz Oscillator is Used to Clock the Asynchronous Timer/Counter2
When the internal RC Oscillator is used as the main clock source, it is possible to
run the Timer/Counter2 asynchronously by connecting a 32 KHz Oscillator between
XTAL1/TOSC1 and XTAL2/TOSC2. But when the internal RC Oscillator is selected
as the main clock source, the CKOPT Fuse does not control the internal capacitors
on XTAL1/TOSC1 and XTAL2/TOSC2. As long as there are no capacitors con-
nected to XTAL1/TOSC1 and XTAL2/TOSC2, safe operation of the Oscillator is not
guaranteed.
Problem fix/Workaround
Use external capacitors in the range of 20 - 36 pF on XTAL1/TOSC1 and
XTAL2/TOSC2. This will be fixed in ATmega8 Rev. G where the CKOPT Fuse will
control internal capacitors also when internal RC Oscillator is selected as main clock
source. For ATmega8 Rev. G, CKOPT = 0 (programmed) will enable the internal
capacitors on XTAL1 and XTAL2. Customers who want compatibility between Rev.
G and older revisions, must ensure that CKOPT is unprogrammed (CKOPT = 1).
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