Hi,

I plan on using the DS1233 (or variant) as a brownout detection to reste
MCLR on a PIC project i have using a 16C73 as Myke Predko explained).  I
remember others on the list having problems with the PIC brwonout circuits,
so this seems like a good method.  However, I wanted to add a battery
backup to the PIC, as this chip will normally be powered by a 9V DC power
supply that is connected to AC.  The 9V will go through a 5V fixed
regulator before the PIC of course.  My question is, what kind of circuit
can I build that would switch in or out a 9v battery as a backup?  I was
thinking a switched MOSFET, except that depending on how variable the 9Vdc
was, the MOSFET might go into the active region and get pretty hot if it
dropped to lets say 8Vdc.

ALso, there aren't any chips similiar to the Dallas brownout chip that have
the battery backup?  I've looked, but the onew with battery backup seem
rather complicated.

Thanks for any thoughts or suggestions!

Rob