You might try using the DalSemi Ibutton / Thermochron.  www.ibutton.com
it has temp/rtc/ram in a can that fits in a coin battery holder and only
needs 1 pin to communicate.  10year life on Lithium battery in the can.

joe


Duilio Foschi wrote:
>
> Are there uPs with clock/calendar as an internal feature ?
>
> Is it advisable to use an external clock/calendar chip anyway ?
>
> Thank you
>
> Duilio Foschi