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'Cheap Reset Circuit -- With slowly rising Vcc (Bat'
1997\08\20@110839 by Scott Walsh

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    Guys,

    I have a problem. My micro is running in a battery operated
    environment where the battery pack is a part of the product.

    When the battery is completely dead ie around 2.4V the micro has
    stopped and so has the resonator. We then begin to charge the battery.

    The volatge starts to rise, at 3.2V we want the micro to startup.

    Do I need to go for a full blown Reset Controller? Or is there a
    simpler (cheaper) method.

    TIA
    Scott.

1997\08\20@120357 by Michael S. Hagberg

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dallas semi has a reset chip that resets at 3.3 vdc. nothing could be
easier to use only 3 pins. i will also say that any time you want to
make something cheaper the reliability goes down faster than the price.
if you are making a million parts the price is important but if you are
making a hundred parts the reliability is important.

michael

At 03:51 PM 8/20/97 -0700, you wrote:
{Quote hidden}

1997\08\20@133702 by Harold Hallikainen

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       Seems like the watchdog timer would take care of this situation.
It would keep resetting the processor, which continues to die until it is
finally brought back to life once the battery voltage is high enough.  Am
I missing something?

Harold



On Wed, 20 Aug 1997 15:51:46 -0700 Scott Walsh
<spam_OUTScott.WALSHTakeThisOuTspamPLANTRONICS.COM> writes:
{Quote hidden}

1997\08\21@002845 by Jim Ham

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I know of two generic methods to solve the problem. One is a transistor and
resistors or a zener as shown in the data sheet. This is the least
expensive (from component cost point of view) method. The other is to use a
power supply supervisor. Check out Maxim and Dallas. This is a more
expensive solution (US$1 to US$2), but they have features that might be
worth the cost: Low power, smaller footprint, more precise, and turn-on
delay. I believe that you will find that you will need to handle reset in
some way. I have a product that I am recalling because of this. Believe me,
it's better to do it right the first time.

The watchdog does _NOT_ work reliable after broun-out. I have no
explaination for this, only experience with 16F84s. The 'F84s will wake up
"sort of" working, and the watchdog will not do a proper reset. Ports wake
up in a funny mode (not documented) and there is a good possibility that
the EEPROM is corrupted.

Regards, Jim

At 03:51 PM 8/20/97 -0700, you wrote:
{Quote hidden}

Jim Ham, Porcine Associates
(415)326-2669 fax(415)326-1071
"http://www.porcine.com"

1997\08\21@073422 by mikesmith_oz
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On 20 Aug 97 at 20:57, Jim Ham wrote:

> I know of two generic methods to solve the problem. One is a
> transistor and resistors or a zener as shown in the data sheet. This
> is the least expensive (from component cost point of view) method.
> The other is to use a power supply supervisor. Check out Maxim and
> Dallas. This is a more expensive solution (US$1 to US$2), but they
> have features that might be worth the cost: Low power, smaller
> footprint, more precise, and turn-on delay. I believe that you will
> find that you will need to handle reset in some way. I have a
> product that I am recalling because of this. Believe me, it's better
> to do it right the first time.
>
> The watchdog does _NOT_ work reliable after broun-out. I have no
> explaination for this, only experience with 16F84s. The 'F84s will
> wake up "sort of" working, and the watchdog will not do a proper
> reset. Ports wake up in a funny mode (not documented) and there is a
> good possibility that the EEPROM is corrupted.

Reset doesn't always seem to remedy some of the problems, either.
How about a 'snap' action on the Vdd pin? (so any voltage below, say
4 volts give 0 v output, then turns on quickly at above 4 volts)
MikeS
<.....mikesmith_ozKILLspamspam@spam@relaymail.net>

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1997\08\21@121848 by Harold Hallikainen

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On Wed, 20 Aug 1997 20:57:30 -0700 Jim Ham <.....jimhamKILLspamspam.....PORCINE.COM> writes:

>The watchdog does _NOT_ work reliable after broun-out. I have no
>explaination for this, only experience with 16F84s. The 'F84s will
>wake up
>"sort of" working, and the watchdog will not do a proper reset. Ports
>wake
>up in a funny mode (not documented) and there is a good possibility
>that
>the EEPROM is corrupted.


       Wow!  Major problem!  I'd hoped that the watchdog timer would
recover from ANYTHING once the power was back up to where the processor
could function.  In another couple products (one using a 68B02, the other
using a PC motherboard), I built a watchdog timer out of a 74HC14 and
several resistors, diodes, and capacitors.  It generates a power-up reset
and works as a watchdog, requiring a pulse to its input every now and
then to prevent it from timing out.  The input is AC coupled so if the
system crashes during a reset it doesn't get stuck.
       As far as eeprom getting corrupted...  that seems to be a way of
life.  In that 68B02 project, I used an MK48T02 "TimeKeeper RAM" (a neat
part, by the way).  It has a real time clock and a little under 2 Kbytes
of battery backed static RAM.  I added gating to the write strobe so the
processor had to enable writing prior to doing a write.  I'm sure it
helps, but every now and then I get a call from a customer with corrupted
set-up data.  I haven't used a PIC with an eeprom in it, so I have no
experience with its protection...

Harold

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