Hi Steve,

if I can all do inside my AT89C4051, why I should spend additional pcb space and cost to use an external RTC ?
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.
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.

The only disadvantage: I need more power.
So in case of power down I use an external timer:
the cheap CD4536.


Peter