Так MEGA же имеет встроенные конденсаторы для работы с "часовым" кварцем, надо токо не забыть фьюзы включить CKORT=0

да, конденсаторы где-то по 22 пФ на кварце нужны. Есть вроде баг с CKOPT - встроенные конденсаторы не включаются, нужно подключать внешние.

да, конденсаторы где-то по 22 пФ на кварце нужны. Есть вроде баг с CKOPT - встроенные конденсаторы не включаются, нужно подключать внешние.

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 connected 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. Cus-
tomers who want compatibility between Rev. G and older revisions, must ensure that
CKOPT is unprogrammed (CKOPT = 1).