On Sun, 26 Nov 2000 06:51:46 -0500, you wrote:

>This is my first attempt at a battery backup strategy. =3D no experience
>
>The requirement is to continue powering a 16f84 + a counter chip + two
>relative encoders, total around 3 to 50 ma at 5v, depending on activity,=
 for
>'a few seconds', then grab the count from the counter and move it to
>internal eeprom, then power everything down until main supply
>returns.....for a price+simplicity
If the PIC can switch off the encoders as soon as the supply
disappears, this will give you a lot more breathing space. Also you
could put the PIC in sleep mode whan you complete the eeprom write, so
the 1-10mS write time happens when the PIC is asleep, to save more
power (I think this works with '84 internal eeprom - it would
certainly work with an external one).

You may want to include some precautions to deal with the eeprom write
being currupted if the supply disappears too quickly, e.g. use 2
alternate data areas with checksums so if a write fails you have the
previous data intact - obviously whether you can do this  depends on
the application.=20

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