Hi Reinhard,

Such a low frequency exeed the maximum rise and fall
time on the XTAL input.
So the internal oscillator can not be used.
You must build an external 32kHz oscillator with a
square wave output connected to XTAL1 (XTAL2 left unconnected)
Ther are many ways to do it:
- with inverters like 74HC04
- with oscillators like CD4046 or CD4047

The internal oscillator was good only down to about 1MHz.

Please can you tell us, why you want to work so slow ?
If you only want to save power, please look at:

http://www.specs.de/~danni/ap...hr4536.htm


Peter