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External real time clock. What to use it?

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julian403

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I was wandering about RTC (external real time clock); for example use a pulse train on a pin which was configured the interrupt (falling or rise) and in the other hand there is the posibility to use the internal time with the time counter overfload.

So, if we have an internal time counter? what to use an external?

I think because the internal time counter is not precise. Because there is a crystal which establishes a clock pulse and whit that and 2^n preescaler there is a limitation.

What do you think?
 

A crystal even multiple of 1s, it have an expected error of few seconds per day. A solution based on microcontroller brings the advantage of allowing either to perform calibration or syncronization by several means, rather than a RTC comprised by a simple oscillator, even accurate.
 
Hi,

An external RTC is usually extremely low power, can work stand alone and has it's own power supply like a coin cell.

Klaus
 
KlausST said:
Hi,

............... and has it's own power supply like a coin cell.

Klaus
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That is indeed the largest benefit of an external RTC. Power interruptions are a fact of life. Any value stored in your micro will be wiped out.
But the RTC will continue running accurately, and when power is restored, the MCU only has to read the RTC registers and the time will be again accurate.
 
How the RTC correct the 1 or 2 secod per day, outdated. I think there is a combinational circuit which every x times it delay 2 second, for example.
 

Re: Double number of pulses per cycle

Even if you are able to determine the need to calibrate the Clock by adding/subtracting a certain amount of seconds per day, it is not accurate. There could remain fractions of a second which were not accounted on that automatic correction. If you want to have an accurate value, you should consider using external signal sources to periodically synch internal RTC with them.
 

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