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'[PIC]: Reset circuits'
2002\08\14@233940 by Brendan Moran

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For using a prepackaged 4-pin reset generator, what would be a good part
for PICs?

- --Brendan
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2002\08\15@001141 by Allan

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I've been using these with excellent results.  They draw less than 40uA.  The
internal PIC BOR consumes over 600uA!
http://canada.digikey.com/scripts/ca/dksus.dll?Detail?Ref=12269&Row=204536

Allan

Brendan Moran wrote:
>
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>
> For using a prepackaged 4-pin reset generator, what would be a good part
> for PICs?
>
> - --Brendan

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2002\08\15@011010 by Tony Nixon

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Brendan Moran wrote:
>
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> For using a prepackaged 4-pin reset generator, what would be a good part
> for PICs?

I've been using the MC34064 T0-92 part on my portable programmer.

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2002\08\15@021710 by Spehro Pefhany

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At 08:38 PM 8/14/02 -0700, you wrote:


>For using a prepackaged 4-pin reset generator, what would be a good part
>for PICs?

Brendan, what do you mean by "4-pin"? Do you require an external reset
switch or WDT?

For an 3-pin reset generator (level detector + timer), Microchip's
MCP809 (SMT, active low output) works nicely, uses little current and
is small.

http://www.microchip.com/download/lit/pline/analog/power/super/11194c.pdf

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
speffspamKILLspaminterlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com
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2002\08\15@023027 by Brendan Moran

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At 02:24 AM 15/08/2002 -0400, you wrote:
{Quote hidden}

An external reset switch was the intention.  I think I can get away without
it, but it would be nicer to have it.

- --Brendan
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2002\08\15@042458 by Spehro Pefhany

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>An external reset switch was the intention.  I think I can get away without
>it, but it would be nicer to have it.

Maxim has the MAX638x series in SC70-4 package, you can also check out
AD.

Best regards,

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2002\08\15@053646 by Michael Rigby-Jones

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{Quote hidden}

I don't suppose you know of any 3volt three pin reset generators that have
an open collector output that can withstand the 13volts Vpp on a PIC?  Seems
like no-one makes such a beast.

Regards

Mike

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2002\08\15@123827 by Brendan Moran

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> I don't suppose you know of any 3volt three pin reset generators
> that have an open collector output that can withstand the 13volts
> Vpp on a PIC?  Seems like no-one makes such a beast.

I'd say don't worry about the open collector, and put a diode in
series with the ouput.

- --Brendan

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2002\08\15@125430 by Dave Tweed

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Brendan Moran <KILLspambmoranKILLspamspamMILLENNIUM.CA> wrote:
> > I don't suppose you know of any 3volt three pin reset generators
> > that have an open collector output that can withstand the 13volts
> > Vpp on a PIC?  Seems like no-one makes such a beast.
>
> I'd say don't worry about the open collector, and put a diode in
> series with the ouput.

The reset generator still needs to withstand 13V if you don't want any
current to flow in the diode when the anode is at Vpp. It's unlikely that a
totem-pole device would meet this requirement with a 3V supply.

-- Dave Tweed

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2002\08\15@134808 by Brendan Moran

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> Brendan Moran <RemoveMEbmoranTakeThisOuTspamMILLENNIUM.CA> wrote:
> > > I don't suppose you know of any 3volt three pin reset
> > > generators that have an open collector output that can
> > > withstand the 13volts Vpp on a PIC?  Seems like no-one makes
> > > such a beast.
> >
> > I'd say don't worry about the open collector, and put a diode in
> > series with the ouput.
>
> The reset generator still needs to withstand 13V if you don't want
> any current to flow in the diode when the anode is at Vpp. It's
> unlikely that a totem-pole device would meet this requirement with
> a 3V supply.

Erm... I think you missed the point.

    |        Vpp
Reset|         |   |
Gen  |---|>|---+---|PIC
    |             |
    |

That should be clearer.  No need to withstand 13V.

- --Brendan

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2002\08\15@153640 by Peter L. Peres

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On Thu, 15 Aug 2002, Dave Tweed wrote:

>Brendan Moran <spamBeGonebmoranspamBeGonespamMILLENNIUM.CA> wrote:
>> > I don't suppose you know of any 3volt three pin reset generators
>> > that have an open collector output that can withstand the 13volts
>> > Vpp on a PIC?  Seems like no-one makes such a beast.
>>
>> I'd say don't worry about the open collector, and put a diode in
>> series with the ouput.
>
>The reset generator still needs to withstand 13V if you don't want any
>current to flow in the diode when the anode is at Vpp. It's unlikely that a
>totem-pole device would meet this requirement with a 3V supply.

One could use an inexpensive NJFET with the gate wired to +Vcc, D and S
between the reset chip and the PIC MCLR pin. Raising S (MCLR) a few volts
above Vcc will close the JFET so the 13V won't reach the regulator. The
reg would see at most a few volts more than Vcc (Vcc + Vg0). A resistor in
the gate is mandatory for when the MCLR is pulled low (probably 1meg or
larger but not really critical). Any JFET would work here. It should
accept -Vgs >= -10V imho. Buying these in bulk should not impact on the
project cost imho. An inexpensive MOSFET could also work here and
eliminate the resistor but beware the reverse bulk diode.

I've also thought of using a single CMOS schmitt (TCxxx) gate as reset
driver/brownout detector. I've also though of using its output to power
the PIC directly for when the MCLR pin is taken. Not tried.

Peter

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2002\08\15@165906 by mike

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On Thu, 15 Aug 2002 09:38:09 -0700, you wrote:

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>> I don't suppose you know of any 3volt three pin reset generators
>> that have an open collector output that can withstand the 13volts
>> Vpp on a PIC?  Seems like no-one makes such a beast.
I normally just put 2K2 or so in series with the reset chip to protect
it from Vpp.

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2002\08\15@193520 by Dave Tweed

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Brendan Moran <TakeThisOuTbmoranEraseMEspamspam_OUTMILLENNIUM.CA> wrote:
{Quote hidden}

Ah. I naturally assumed that since the OP wanted an open-collector
driver, he wanted to sink current from the reset pin, not source
current to it.

-- Dave Tweed

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2002\08\15@194403 by Brendan Moran

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> Ah. I naturally assumed that since the OP wanted an open-collector
> driver, he wanted to sink current from the reset pin, not source
> current to it.

Fair enough.  In that case, a single P-channel FET attached to the
reset generator should do the trick nicely.

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2002\08\16@040443 by Michael Rigby-Jones

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> -----Original Message-----
> From: Brendan Moran [SMTP:bmoranEraseMEspam.....MILLENNIUM.CA]
> Sent: Thursday, August 15, 2002 5:38 PM
> To:   EraseMEPICLISTspamMITVMA.MIT.EDU
> Subject:      Re: [PIC]: Reset circuits
>
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
>
> > I don't suppose you know of any 3volt three pin reset generators
> > that have an open collector output that can withstand the 13volts
> > Vpp on a PIC?  Seems like no-one makes such a beast.
>
> I'd say don't worry about the open collector, and put a diode in
> series with the ouput.
>
And a pull down resistor.  This is what we have done in the past but our
board space is often so tight that even a couple of extra tiny surface mount
components can make things awkward.  Also the MCLR voltage thresholds
preclude the use of a cheap silicon diode at 3.3volts or below, you have to
use a (more expensive) Schottky diode.

Regards

Mike

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2002\08\16@040823 by Michael Rigby-Jones

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> -----Original Message-----
> From: Mike Harrison [SMTP:RemoveMEmikeEraseMEspamEraseMEwhitewing.co.uk]
> Sent: Thursday, August 15, 2002 9:59 PM
> To:   RemoveMEPICLISTspam_OUTspamKILLspamMITVMA.MIT.EDU
> Subject:      Re: [PIC]: Reset circuits
>
> On Thu, 15 Aug 2002 09:38:09 -0700, you wrote:
>
> >-----BEGIN PGP SIGNED MESSAGE-----
> >Hash: SHA1
> >
> >> I don't suppose you know of any 3volt three pin reset generators
> >> that have an open collector output that can withstand the 13volts
> >> Vpp on a PIC?  Seems like no-one makes such a beast.
> I normally just put 2K2 or so in series with the reset chip to protect
> it from Vpp.
>
>
We discussed this in the office at the time, and while the general thoughts
were that it would work, I get an uncomfortable feeling driving 13 volts
(albeit current limited) back into the output.  Probably just me being
silly,

Mike

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2002\08\16@040835 by Michael Rigby-Jones

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{Quote hidden}

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2002\08\16@043902 by Alan B. Pearce

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>Erm... I think you missed the point.
>
>     |        Vpp
>Reset|         |   |
>Gen  |---|>|---+---|PIC
>     |             |
>     |
>
>That should be clearer.  No need to withstand 13V.

How is this going to reset the PIC ????

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2002\08\17@165421 by Peter L. Peres

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On Thu, 15 Aug 2002, Brendan Moran wrote:

>Erm... I think you missed the point.
>
>     |        Vpp
>Reset|         |   |
>Gen  |---|>|---+---|PIC
>     |             |
>     |
>
>That should be clearer.  No need to withstand 13V.

That won't work easily. You need a pulldown on MCLR and pullup on the
output of the o.c. reset generator. and that makes the diode critical
because Vih on MCLR is Vdd-0.4V.

Peter

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