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'Startup problems with 16C71'
1997\01\10@051059 by Werner Terreblanche

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My battery powered 16C71 application is experiencing startup
problems.  Every tenth or so time when I switch on power to the
circuit, it just wouldn't start up.  I've got a watchdog implemented
and I am enabling the startup timer.   Could the fact that I am
enabling the startup timer have something to do with the problem?  I
remember reading something about the relationship between the startup
timer and slow rising supply voltages and some sort of problem
associated with this, but I can not for the life of me remember
exactly what it was.  I even tried using the PIC16C711 with brownout
protection, but that also didn't seem to help.  Any advice would
really be appreciated.

Rgds
Werner
--
Werner Terreblanche     http://www.aztec.co.za/users/werner
spam_OUTwterrebTakeThisOuTspamplessey.co.za (work)  OR  .....wernerKILLspamspam@spam@aztec.co.za  (home)
Plessey SA, PO Box 30451,Tokai 7966, Cape Town, South Africa
or (Suite 251, PostNet X5061, Stellenbosch, 7599)
Tel +27 21 7102251   Fax +27 21 721278   Cell +27 837255164
------------------------------------------------------------

1997\01\10@073517 by Lee Johnston

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Werner Terreblanche wrote:

> My battery powered 16C71 application is experiencing startup
> problems.  Every tenth or so time when I switch on power to the
> circuit, it just wouldn't start up...

I have had some of the same problems and have found that maxim's max709
reset chip works well for me.  In addition to providing a better reset to
the pic, it also provides better brownout protection than the circuits
shown in microchip's literature.

Lee Johnston
Blacksburg, VA

1997\01\10@100958 by timetech

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Werner Terreblanche wrote:
>
> My battery powered 16C71 application is experiencing startup
> problems.  Every tenth or so time when I switch on power to the
> circuit, it just wouldn't start up.

Werner:

Are you switching the battery with a switch? If you are, you need to
deal with the enormous trash that accompanies the switch closure; many
inexpensive switches bounce around for a long time. A power supply with
the AC line switched doesn't usually exhibit poor behavior until
powerdown, if at all (depends on the supply). This can be a problem if
you expect to preserve information while powered down. Dallas has done a
good job of dealing with this, and you can check their stuff for a good
start at what needs to be done in this case.

We in general try to avoid the battery switch problem by either leaving
the system on and asleep or allowing the system to control it's own
power through external means. In any system where you switch battery
power, you will probably need an external reset of one form or another,
either directly to the PIC chip or in the form of controled turn on of
the external power devices. (Allowing the PIC chip to control the system
powerdown guarantees the program condition at that point.)

-- Tom Rogers  VP - R&D  Time Tech Inc.

1997\01\10@101001 by timetech

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Lee Johnston wrote:

> I have had some of the same problems and have found that maxim's max709
> reset chip works well for me.  In addition to providing a better reset to
> the pic, it also provides better brownout protection than the circuits
> shown in microchip's literature.
>
> Lee Johnston
> Blacksburg, VA

Yup, good choice. We've used exactly the same setup.

Tom Rogers  Time Tech Inc.

1997\01\13@023934 by Werner Terreblanche

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Werner Terreblanche wrote:
>
> My battery powered 16C71 application is experiencing startup
> problems.  Every tenth or so time when I switch on power to the
> circuit, it just wouldn't start up.

Werner:

> Are you switching the battery with a switch? If you are, you need to
> deal with the enormous trash that accompanies the switch closure; many
> inexpensive switches bounce around for a long time. A power supply
> with the AC line switched doesn't usually exhibit poor behavior until
> powerdown, if at all (depends on the supply). This can be a problem if
> you expect to preserve information while powered down. Dallas has done
> a good job of dealing with this, and you can check their stuff for a
> good start at what needs to be done in this case.

Tom

Yes I am switching the battery with a switch.  I really hoped that
there would have been some sort of software solution, because I've
already got a bunch of PCB's made.

I experimented with it over the weekend, and it seems that switching the
Brownout detect and the Power up timer does reduce the effect quite
dramatically compared to leaving them switched off.  However, I'm not
sure if it completely solves the problem.

Thank you for your advice

Werner
--
Werner Terreblanche     http://www.aztec.co.za/users/werner
wterrebspamKILLspamplessey.co.za (work)  OR  .....wernerKILLspamspam.....aztec.co.za  (home)
Plessey SA, PO Box 30451,Tokai 7966, Cape Town, South Africa
or (Suite 251, PostNet X5061, Stellenbosch, 7599)
Tel +27 21 7102251   Fax +27 21 721278   Cell +27 837255164
------------------------------------------------------------

1997\01\13@082849 by Fred Thompson

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Werner,

       Have you tried adding a nice large capacitor in parallel with
your switch.  Might help reduce the effects of the bounce a little.

Fred Thompson
EraseMEfthompsospam_OUTspamTakeThisOuTmail.win.org


On Mon, 13 Jan 1997, Werner Terreblanche wrote:

{Quote hidden}

1997\01\13@083056 by timetech

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Werner Terreblanche wrote:

> Yes I am switching the battery with a switch.  I really hoped that
> there would have been some sort of software solution, because I've
> already got a bunch of PCB's made.

<snippp>

Oops. Oh, well. There are still some things you can do. The first is to
change your switch. If you don't use much more than 50 mA you can try a
switch with gold crosspoint contacts. You don't need the gold, but the
mechanism of these switches is usually of higher quality, with more
attention to the details of the switching transition. You could also
contact your switch manufacturer for advice, which I'm sure they'ed be
happy to give. As a last resort, try increasing the cap on the power
input (you do have a cap on the PIC side of the switch, yes?).

-- Tom Rogers

1997\01\13@185301 by id John Philip Bodger

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>Werner Terreblanche wrote:
>>
>> My battery powered 16C71 application is experiencing startup
>> problems.  Every tenth or so time when I switch on power to the
>> circuit, it just wouldn't start up.
>
>Werner:

Not the same chip, but with the 16C84 battery powered, I had problems with
corruption of eeprom values that were copied to ram and back at startup
because of the low power consumption of my circuit ment that if the user
quickly turned power on and off the power would ramp up quickly then decay
slowly because of the power supply capacitors held too much charge (but that
charge was needed when the circuit was in full operation as I switch several
amps through IR emitters).
Anyway, to get around it, in my 'mark 2' version, I have used a comparator
LM393 to sense the battery voltage input to the v.reg dropped by a simple
potential divider, and compare it to the output from the (low drop-out) 5v
v.reg; such that when the input drops below 6 volts the comparitor output
asserts /MCLR, and with added hysteresis will not un-assert it until the
v.reg input goes above 7 volts.
Works a treat and no problems since. I also use the output to drive a low
current led to give a visual low battery warning (the comparitor gets it's
power from the regulated 5v).

Hope this idea is of some help.

All the best.

Dave.

P.S. sorry I couldn't think of a software solution.  :-(

1997\01\13@200152 by John Payson

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> > Yes I am switching the battery with a switch.  I really hoped that
> > there would have been some sort of software solution, because I've
> > already got a bunch of PCB's made.

>         Have you tried adding a nice large capacitor in parallel with
> your switch.  Might help reduce the effects of the bounce a little.

Actually, my guess is that it would make the problem worse.  On quite a
number of micros with built-in power-up-detect circuits, the VDD voltage
must get down very close to ground before power-up in order to ensure that
the power-up circuit trips.  On many CPU driven devices, however, there is
not really anything to load down the supply once the CPU has stopped running.
As a consequence, devices' filter caps can sometimes hover around a volt for
quite some time, making startup unreliable.

A remedy for this which I have seen in a number of consumer products is to
use a SPDT switch; the common wire should go to the circuit's power-supply
input, one edge to the battery, and the other edge to ground.  Thus, when
the switch is turned off it will ensure that the power-supply voltage to
the chips in the device goes all the way to zero.  With luck you'll be able
to add something like this to your board (if you used a SPDT or DPDT switch
and left the other pins unconnected).

1997\01\14@022730 by Werner Terreblanche

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>> Yes I am switching the battery with a switch.  I really hoped that
>> there would have been some sort of software solution, because I've
>> already got a bunch of PCB's made.


Thanks to everyone that made suggestion.  I've got a whole lot
of things to try out now.


terogers <KILLspamtimetechKILLspamspamOP.NET> wrote:

> Oops. Oh, well. There are still some things you can do. The first is
> to change your switch. If you don't use much more than 50 mA you can
> try a switch with gold crosspoint contacts. You don't need the gold,
> but the mechanism of these switches is usually of higher quality, with
> more attention to the details of the switching transition. You could
> also contact your switch manufacturer for advice, which I'm sure
> they'ed be happy to give. As a last resort, try increasing the cap on
> the power input (you do have a cap on the PIC side of the switch,
> yes?).

I'm quite convinced as well now that the switch is partly to blame,
because if I elminate the switch and directly make the contact by
pressing the battery on its clip, the PIC always starts up.  And yes,
I do have a cap on the PIC side of the regulator and on the switch
side.  I'll investigate if changing their values make any
improvements.  Changing the switch might be more difficult, because
I'm not sure if it would be easy to source another right angle PCB
mount switch of the same dimensions that is gold plated.

John Payson <RemoveMEsupercatTakeThisOuTspamMCS.NET> wrote:

{Quote hidden}

This suggestion by John Payson sounds like an easy enough hardware
modification to implement, since I'm already using a SPDT switch and
there is ground available near the switch.  I'll definetely try this.


David John Philip Bodger <spamBeGonedavebodgerspamBeGonespamMAIL.BOGO.CO.UK> wrote

> Not the same chip, but with the 16C84 battery powered, I had problems
> with corruption of eeprom values that were copied to ram and back at
> startup because of the low power consumption of my circuit meant that
> if the user quickly turned power on and off the power would ramp up
> quickly then decay slowly because of the power supply capacitors held
> too much charge (but that charge was needed when the circuit was in

This might be what is happening on my boards as well.  My circuit is
drawing very little current and it looks like I only see this effect
when you switch the circuit on and off repeatedly.  I suppose in my
case it might not be neccessary to go to the extremes of having to
monitor the battery voltage because I'm hoping the suggestion made by
John Payson will also completely discharge the capacitors when you
switch the circuit off.  Thank you for your suggestion.  I'll certainly keep it
in
mind if I ever need to make modifications to the board, or if this
switch modification doesn't want to work.  :)

Rgds
Werner
--
Werner Terreblanche     http://www.aztec.co.za/users/werner
TakeThisOuTwterrebEraseMEspamspam_OUTplessey.co.za (work)  OR  RemoveMEwernerspamTakeThisOuTaztec.co.za  (home)
Plessey SA, PO Box 30451,Tokai 7966, Cape Town, South Africa
or (Suite 251, PostNet X5061, Stellenbosch, 7599)
Tel +27 21 7102251   Fax +27 21 721278   Cell +27 837255164
------------------------------------------------------------

1997\01\14@083211 by Werner Terreblanche

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I just received the Third Edition 1996 Technical Library on CD from
Microchip (thanks Microchip :) and on it there were a complete
application not  (AN607) on Power-up Trouble Shooting.
I quote from AN607:


Q. The device was powered-down and then pow-ered back up, but the
device does not oper-ate. What could be wrong. A. Possibilities
include:

1. If power was applied to an I/O pin when the device was
"powered-down", the device would be powered through the I/O pin. The
internal logic is not actually powered-down, and Power-on Reset (POR)
will not occur.

2.When VDD was powered-down, VDD was not given enough
time to settle to 0V.

3. The VDD ramp rate is too slow.
--
Werner Terreblanche     http://www.aztec.co.za/users/werner
wterrebEraseMEspam.....plessey.co.za (work)  OR  EraseMEwernerspamaztec.co.za  (home)
Plessey SA, PO Box 30451,Tokai 7966, Cape Town, South Africa
or (Suite 251, PostNet X5061, Stellenbosch, 7599)
Tel +27 21 7102251   Fax +27 21 721278   Cell +27 837255164
------------------------------------------------------------

1997\01\14@083215 by Michael Yano

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At 09:38 AM 1/14/97 GMT+2, you wrote:
> Yes I am switching the battery with a switch.  I really hoped that
> there would have been some sort of software solution, because I've
> already got a bunch of PCB's made.
>



I've used the watchdog timer to prevent the power on lockup on some of the
other chips.

Thanks.


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