17

ATmega8(L)

2486QS–AVR–10/06

Erratas

The revision letter in this section refers to the revision of the ATmega8 device.

ATmega8

Rev. D to I

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

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).