Thanks mister_e

I implemented your sugestions but even though the PCF refuses to work.

I also started to suspect of PCF sample chip I received from Philips distributor, because is not normal the logic level never reaches 0 (ground) even without pull-up resistors.

So... I bought a new chip and... VOILÁ

I suppose that sample chips are like PORT WINE, some are good and some aren't.

Sometimes, no matter how much time you have spent in you life dealing with electronics,always keep forgetting that it may be some problem with materials. I need to pay more attention to this kind of things.

Once again thanks a lot for your kind assistance and ... please accept my season's greetings

NOMADA