> I want to sound an alert when it drops below 1000 or 800 RPM.
>
> BTW, this will be done with two (redundant - running side-by-side)
> fans, so I'm not sure if the watchdog idea would work or not.

Use INT0 and INT1 as the inputs from the fans and set the post-
scaler for a WDT period longer than expected fan pulses. Alternate
between the two inputs at every CLRWDT

Scenario - both fans are running normally. INT0 is the active interrupt
source. Pulse arrives, interrupt does a CLRWDT, enables INT1 as the
active interrupt source, and so on alternating. If one fan fails, it will 
not
cause a CLRWDT to be executed in its alloted time as the active source

So, if nominal WDT period is 18ms and you expect a pulse every 46ms
(1300 rpm), then a WDT post-scaler of 1:4 (= 72ms) will cause an alarm
if the selected fan drops to 833 rpm

Examine RCON,TO prevent a full-scale initialisation

wbr 

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