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M41T81S RTC chip. Remembering time on power down.

Question asked by Toru Fujinami on Oct 28, 2017

I am using M41T81S chip for a RTC.

I am having a issue keeping a time on power down.

 

I borrowed the circuit from following location.

http://www.niell.org/nixie_3/NixieClock5-1.bmp 

Instead of C2 in the picture, I am using 1F super Cap.

 

Even on power down condition (removing +5V), M41T81S should continue counting time as long as proper voltage applied to Vbat.

On my setupt, I verified that Vbat remains 3.3V at all time, but timer resets to 00:00:00 as soon as main supply is removed.

 

Would you please help me solving this issue?

Also, is there sample code I can follow to communicate with this chip?

Attached "Code.PNG" is a startup sequence I am using to start up this RTC chip.

 

Thank you,

Toru

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