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'CPU monitor devices?'
1998\12\31@121001 by John Payson

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Does anyone have any ideas about CPU monitoring devices that would
meet the following criteria?  Some 8-pin devices I've seen come sorta
close, but I'd prefer something more like the following:

-1- Relatively short (e.g. 1-10ms) reset pulse; many of the devices that
   I've seen have a 250ms reset pulse, which adds to the time the device
   will be inoperable if anything goes wrong.  Obviously the reset timer
   should not start until power is within tolerance.

-2- Active high and active low outputs (so as to be useable with 8x51's
   as well as PICs).

-3- An "intelligent" watchdog circuit which would not be satisfied with
   random port flailing.  Perhaps requiring that feeding pulses come in
   pairs, with the first two pulses 10us or less apart, and with at
   least 100us between pairs.  Keeping the watchdog fed in such a scheme
   should be about as easy as it is with existing parts, but the device
   would be more likely to detect a problem which caused the port pins
   to flail randomly.

-4- A "pushbutton reset" circuit which can accept even short pulses on
   the input (e.g. which can be hooked up to /PSEN on an 8x51 to reset
   the CPU if it tries to run code out of external memory).

Anyone know of any good devices that fit that bill?  A fifth feature
which would be even cooler if anyone makes it would be:

-5- A built-in voltage regulator which could briefly switch off (and
   shunt the output to ground) in case of trouble.  "Trouble" in this
   case would most likely be a reset (of whatever sort) which does not
   result in the CPU feeding the watchdog within a reasonable time, or
   else an asserted input on a "force power cycle" pin.  Since CPU's
   can land in states where only a power-down/power-up reset will fix
   them, it would be useful to have hardware that could handle that
   automatically.

1998\12\31@133320 by Andy Kunz

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At 11:09 AM 12/31/98 -0600, you wrote:
>Does anyone have any ideas about CPU monitoring devices that would
>meet the following criteria?  Some 8-pin devices I've seen come sorta
>close, but I'd prefer something more like the following:

<snip>

Why not a 12C part?

Andy
==================================================================
Andy Kunz - Statistical Research, Inc. - Westfield, New Jersey USA
==================================================================

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