wich sleep mode will keep a date/time running?

Hi. I'm working at a project where I need to keep the date/time working after the restart. Could anybody tell me how to do it or give me a clue.

Tks a lot

Sounds like you need an RTC chip...?

Hi.. I have never worked with that. Actually don't know anything about it...

I thought the arduino in sleep mode could do some job while sleeping

I'll read about it.. tks!

If you want to work in scales of more than milliseconds then you really require an RTC chip. If you want to keep track of the time and date while the Arduino is either busy doing something else, sleeping, or even turned off, then you require an RTC chip.

The most common is the DS1307, and there are millions of shields with them on around the place.