DS1302 on battery or super cap backup
John Jenkins
Posts: 12
I have a DS1302 in a project. Everything works perfectly, except that when power is removed from the system, and then restored, the clock begins counting at the time when power was removed. i.e. even though the DS1302 is "backed up" with a supercap or a battery (I've tried both, connected as per the datasheet) it doesn't continue to keep time when VCC2 is removed. From everything I have read in the datasheet and in the forums, I believe the chip should continue to count time when running on power from VCC1, rather than just starting up again at the last time when it had power from VCC2. · Is that correct?· If so, any idea what I'm doing wrong?
Thanks!
Thanks!
Comments
What does your code look like? You have to tell the DS1302 how you want it to "trickle charge".
See page 7 and page 9 of the datasheet.... http://pdfserv.maxim-ic.com/en/ds/DS1302.pdf
To confirm your code setup, try connecting the Anode of a small low current (2mA) LED to Vcc1 instead of your battery/capacitor while connecting the Cathode of the LED to GND to make sure the code is indeed doing what you want it to do.
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Beau Schwabe
IC Layout Engineer
Parallax, Inc.
Post Edited (Beau Schwabe (Parallax)) : 6/27/2008 5:56:51 AM GMT
I added the following code (included for others who might have this problem) and that did the trick. Now it works perfectly.
Thanks Beau!
' enable trickle charger for 1 diode, 2K ohm resistor
HIGH CS1302 ' Ready for transfer
SHIFTOUT DataIO, CLOCK, LSBFIRST, [noparse][[/noparse]$8E, $0] ' Enable write, control = 0
LOW CS1302 ' Reset RTC
HIGH CS1302 ' Ready for transfer
SHIFTOUT DataIO, CLOCK, LSBFIRST, [noparse][[/noparse]$90,$A5] 'Write trickle = %10100101
LOW CS1302