Peter Dannegger wrote:
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>if I can all do inside my AT89C4051, why I should spend additional pcb >space and cost to use an external RTC ?

Assuming you don't need external RAM OK, but I need external and backed RAM


>Then I lose also the chance to correct deviation in software
>without an instable trimmed capacitor.
>Also my software RTC can serve calculation of weekday
>and daylight saving.

Doesn't change the clever tricks in software ! but saves interrupt handling when you are really time critical. OK if you are building a clock use software, but what about when you are in a high speed problem ?>

>Most RTC are not easy to read and set (4-bit BCD coded,
>very particular serial protocol) , so no significant code
>space and CPU time saved.

Code is pretty easy really.


Peter