At 11:33 AM 7/30/2004 -0500, you wrote:
>  frequently for my happiness) it gets over >100C due to chassis
>changes.  I have on the re-design list to add an additional temperature
>sensor to monitor the controller and give it an early warning that the
>ambient temperature is rising above 85C so the system can attempt to
>modulate the temperature a bit.

That sounds reasonable.

>What seems to be happening with the 'HC705 is that its clock circuit gives
>up and the part just stops running.  The xtal is rated for 125C and a=
 little
>testing showed me the caps were OK too.

Well, it's quite possible that the chip and the crystal and the caps will
all meet their specifications at 100-125=B0C, but they will fail to work
together. Possible enough that you'll probably find it difficult to
impossible to get any guarantees from the suppliers.

You might want to look at swapping the crystal for a ceramic resonator
with built-in capacitors, since frequency accuracy isn't a big deal for
you (or use an internal RC clock, even better). There are reportedly
(on very good authority) "issues" with the clock oscillator design on
certain micros..

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the=
 reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

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