The most suitable way is always, use simple a timer interrupt and count seconds, minutes, hours internal.

It give the easiest software, less overhead, no protocol conversion.

Furthermore the time was always accessible inside the SRAM, no need to poll an external RTC again and again and again.

Furthermore you have the freedom to implement functions, which are not supported by RTC chips, e.g. weekday calculation, daylight saving time.

Further explanations can be seen at:

http://www.specs.de/users/dan...curacy.htm


Peter