Lpc2000

Hi,
I'm working on an LPC2138 design and just moved
into ESD testing. After some ESD hits there was
no damage, but the processor would be left not 
running.

Implementing the internal watchdog didn't fix this.

Apparently there are ways to nail a 2138 with ESD
that must stop the processor clock and thus also
prevent the internal watchdog from working.

My solution is an external supervisor chip with a
watchdog function that I would keep strobed with
some line from the micro.

I know this will work because when an ESD hit 'stuns'
the LPC2138 I can restart it by toggling reset.

The problem is I want to use the internal flash loader
to do the factory program load for my board.

The flash loader will not keep my external watchdog strobed
and will not be able to avoid a reset as a result. So the
external watchdog will keep it from working.

Question: Does the phillips flash loader toggle and pin
regularly that I could use for this strobe?

Can I hook it somehow to make it pet the dog?

Any ideas?

Landrum

Hello,

bad foul!!! I think there is no software solution (except hacking the
philips bootloader). You could insert a single gate (NAND) into the
/reset signal that disables /reset (=1) while P0.14 (for entering
bootloader programming mode) is low during programming. 

  Sten

--- In lpc2000@yahoogroups.com, "lhaddix" <lhaddix@i...> wrote:

>
> Hi,
> I'm working on an LPC2138 design and just moved
> into ESD testing. After some ESD hits there was
> no damage, but the processor would be left not 
> running.
> 
> Implementing the internal watchdog didn't fix this.
> 
> Apparently there are ways to nail a 2138 with ESD
> that must stop the processor clock and thus also
> prevent the internal watchdog from working.
> 
> My solution is an external supervisor chip with a
> watchdog function that I would keep strobed with
> some line from the micro.
> 
> I know this will work because when an ESD hit 'stuns'
> the LPC2138 I can restart it by toggling reset.
> 
> The problem is I want to use the internal flash loader
> to do the factory program load for my board.
> 
> The flash loader will not keep my external watchdog strobed
> and will not be able to avoid a reset as a result. So the
> external watchdog will keep it from working.
> 
> Question: Does the phillips flash loader toggle and pin
> regularly that I could use for this strobe?
> 
> Can I hook it somehow to make it pet the dog?
> 
> Any ideas?
> 
> Landrum
>

IIRC some external watchdog timer chips force a reset on timeout only
if their input pin is held high or low for too long a period.  If the
pin is left floating, the watchdog function is disabled.  See the TI
TPS382x family info (SLVA039 section 10).  The boot loader most likely
leaves unused GPIO pins unconfigured so they should be in their
default mode as inputs.  If that case the floating connection to the
watchdog chip should disable the timed reset function.

Good luck
-Bill Knight
R O SoftWare &
http://www.theARMPatch.com

On Mon, 17 Oct 2005 12:17:58 -0000, bdmlpc wrote:

>Hello,

>bad foul!!! I think there is no software solution (except hacking the
>philips bootloader). You could insert a single gate (NAND) into the
>/reset signal that disables /reset (=1) while P0.14 (for entering
>bootloader programming mode) is low during programming. 

>  Sten

>--- In lpc2000@yahoogroups.com, "lhaddix" <lhaddix@i...> wrote:
>>
>> Hi,
>> I'm working on an LPC2138 design and just moved
>> into ESD testing. After some ESD hits there was
>> no damage, but the processor would be left not 
>> running.
>> 
>> Implementing the internal watchdog didn't fix this.
>> 
>> Apparently there are ways to nail a 2138 with ESD
>> that must stop the processor clock and thus also
>> prevent the internal watchdog from working.
>> 
>> My solution is an external supervisor chip with a
>> watchdog function that I would keep strobed with
>> some line from the micro.
>> 
>> I know this will work because when an ESD hit 'stuns'
>> the LPC2138 I can restart it by toggling reset.
>> 
>> The problem is I want to use the internal flash loader
>> to do the factory program load for my board.
>> 
>> The flash loader will not keep my external watchdog strobed
>> and will not be able to avoid a reset as a result. So the
>> external watchdog will keep it from working.
>> 
>> Question: Does the phillips flash loader toggle and pin
>> regularly that I could use for this strobe?
>> 
>> Can I hook it somehow to make it pet the dog?
>> 
>> Any ideas?
>> 
>> Landrum
>>







> 
>Yahoo! Groups Links



>

Ok, there is a software solution... ;-)

   Sten

--- In lpc2000@yahoogroups.com, "Bill Knight" <BillK@t...> wrote:

>
> IIRC some external watchdog timer chips force a reset on timeout only
> if their input pin is held high or low for too long a period.  If the
> pin is left floating, the watchdog function is disabled.  See the TI
> TPS382x family info (SLVA039 section 10).  The boot loader most likely
> leaves unused GPIO pins unconfigured so they should be in their
> default mode as inputs.  If that case the floating connection to the
> watchdog chip should disable the timed reset function.
> 
> Good luck
> -Bill Knight
> R O SoftWare &
> http://www.theARMPatch.com
> 
> 
> On Mon, 17 Oct 2005 12:17:58 -0000, bdmlpc wrote:
> 
> >Hello,
> 
> >bad foul!!! I think there is no software solution (except hacking the
> >philips bootloader). You could insert a single gate (NAND) into the
> >/reset signal that disables /reset (=1) while P0.14 (for entering
> >bootloader programming mode) is low during programming. 
> 
> >  Sten
> 
> >--- In lpc2000@yahoogroups.com, "lhaddix" <lhaddix@i...> wrote:
> >>
> >> Hi,
> >> I'm working on an LPC2138 design and just moved
> >> into ESD testing. After some ESD hits there was
> >> no damage, but the processor would be left not 
> >> running.
> >> 
> >> Implementing the internal watchdog didn't fix this.
> >> 
> >> Apparently there are ways to nail a 2138 with ESD
> >> that must stop the processor clock and thus also
> >> prevent the internal watchdog from working.
> >> 
> >> My solution is an external supervisor chip with a
> >> watchdog function that I would keep strobed with
> >> some line from the micro.
> >> 
> >> I know this will work because when an ESD hit 'stuns'
> >> the LPC2138 I can restart it by toggling reset.
> >> 
> >> The problem is I want to use the internal flash loader
> >> to do the factory program load for my board.
> >> 
> >> The flash loader will not keep my external watchdog strobed
> >> and will not be able to avoid a reset as a result. So the
> >> external watchdog will keep it from working.
> >> 
> >> Question: Does the phillips flash loader toggle and pin
> >> regularly that I could use for this strobe?
> >> 
> >> Can I hook it somehow to make it pet the dog?
> >> 
> >> Any ideas?
> >> 
> >> Landrum
> >>
> 
> 
> 
> 
> 
> 
> 
> > 
> >Yahoo! Groups Links
> 
> 
> 
> >
>

Did anyone else experience the same problem (the LPC2138 stops running and 
the wachdog doesn\ufffdt restart it) ?


----- Original Message ----- 

From: "lhaddix" <lhaddix@...>
To: <lpc2000@yahoogroups.com>
Sent: Monday, October 17, 2005 8:27 AM
Subject: [lpc2000] External watchdog and flash loader


> Hi,
> I'm working on an LPC2138 design and just moved
> into ESD testing. After some ESD hits there was
> no damage, but the processor would be left not
> running.
>
> Implementing the internal watchdog didn't fix this.
>
> Apparently there are ways to nail a 2138 with ESD
> that must stop the processor clock and thus also
> prevent the internal watchdog from working.
>
> My solution is an external supervisor chip with a
> watchdog function that I would keep strobed with
> some line from the micro.
>
> I know this will work because when an ESD hit 'stuns'
> the LPC2138 I can restart it by toggling reset.
>
> The problem is I want to use the internal flash loader
> to do the factory program load for my board.
>
> The flash loader will not keep my external watchdog strobed
> and will not be able to avoid a reset as a result. So the
> external watchdog will keep it from working.
>
> Question: Does the phillips flash loader toggle and pin
> regularly that I could use for this strobe?
>
> Can I hook it somehow to make it pet the dog?
>
> Any ideas?
>
> Landrum
>
>
>
>
>
>
>
> Yahoo! Groups Links
>
>
>
>
>
>
>
>
> Esta mensagem foi verificada pelo E-mail Protegido Terra.
> Scan engine: McAfee VirusScan / Atualizado em 14/10/2005 / Vers\ufffdo: 
> 4.4.00/4605
> Proteja o seu e-mail Terra: http://mail.terra.com.br/
>

Yes, with a LPC2124 we had some similar problems in a design.

Marcio Zaquela wrote:
> Did anyone else experience the same problem (the LPC2138 stops running and 
> the wachdog doesn\ufffdt restart it) ?
> 
> 
> ----- Original Message ----- 
> From: "lhaddix" <lhaddix@...>
> To: <lpc2000@yahoogroups.com>
> Sent: Monday, October 17, 2005 8:27 AM
> Subject: [lpc2000] External watchdog and flash loader
> 
> 
> 
>>Hi,
>>I'm working on an LPC2138 design and just moved
>>into ESD testing. After some ESD hits there was
>>no damage, but the processor would be left not
>>running.
>>
>>Implementing the internal watchdog didn't fix this.
>>
>>Apparently there are ways to nail a 2138 with ESD
>>that must stop the processor clock and thus also
>>prevent the internal watchdog from working.
>>
>>My solution is an external supervisor chip with a
>>watchdog function that I would keep strobed with
>>some line from the micro.
>>
>>I know this will work because when an ESD hit 'stuns'
>>the LPC2138 I can restart it by toggling reset.
>>
>>The problem is I want to use the internal flash loader
>>to do the factory program load for my board.
>>
>>The flash loader will not keep my external watchdog strobed
>>and will not be able to avoid a reset as a result. So the
>>external watchdog will keep it from working.
>>
>>Question: Does the phillips flash loader toggle and pin
>>regularly that I could use for this strobe?
>>
>>Can I hook it somehow to make it pet the dog?
>>
>>Any ideas?
>>
>>Landrum
>>


-- 
/************************************************
 Do you need a tiny and efficient real time
 operating system (RTOS) with a preemtive
 multitasking for LPC2000 or AT91SAM7?

   http://nanortos.net-attack.de/

 Or some open-source tools and code for LPC2000?

   http://www.net-attack.de/

************************************************/

Sten,
What do you mean 'bad foul!!!' my design or this situation?

I think I will add circuitry to inhibit the external watchdog
when P0.14 is low. I also want to inhibit the external watchdog
when my 20pin JTAG is in use. 

What can I sense to tell if the JTAG port is connected to an 
emulator? 

I thought about counting on one of it's many grounds
pulling a pin low, but would rather use something that didn't
depend on certain grounds being connected inside the emulator
pod.

I guess as Marcio points out the larger issue is why are there
situations where the internal watchdog can't reset the micro.
Unfortunately this is probably a feature of the LPC design.

Microchip uses an internal RC for thier watchdog which is not
dependant of the system clock for instance.

I think what happens is it's possible for an ESD hit to stop
the crystal osc on the LPC such that reset is needed to restart
the oscillator, but there can be no watchdog reset without a system 
clock.

I've considered using an external osc to feed the ARM, but don't
wish to do this. I can't be sure it would fix the problem without
mocking it up and then blasting with the static gun, but I know that
toggling reset from outside will restart the clock. 

Landrum


--- In lpc2000@yahoogroups.com, Sten <list@n...> wrote:
>
> Yes, with a LPC2124 we had some similar problems in a design.
> 
> Marcio Zaquela wrote:
> > Did anyone else experience the same problem (the LPC2138 stops 
running and 

> > the wachdog doesn´t restart it) ?
> > 
> > 
> > ----- Original Message ----- 
> > From: "lhaddix" <lhaddix@i...>
> > To: <lpc2000@yahoogroups.com>
> > Sent: Monday, October 17, 2005 8:27 AM
> > Subject: [lpc2000] External watchdog and flash loader
> > 
> > 
> > 
> >>Hi,
> >>I'm working on an LPC2138 design and just moved
> >>into ESD testing. After some ESD hits there was
> >>no damage, but the processor would be left not
> >>running.
> >>
> >>Implementing the internal watchdog didn't fix this.
> >>
> >>Apparently there are ways to nail a 2138 with ESD
> >>that must stop the processor clock and thus also
> >>prevent the internal watchdog from working.
> >>
> >>My solution is an external supervisor chip with a
> >>watchdog function that I would keep strobed with
> >>some line from the micro.
> >>
> >>I know this will work because when an ESD hit 'stuns'
> >>the LPC2138 I can restart it by toggling reset.
> >>
> >>The problem is I want to use the internal flash loader
> >>to do the factory program load for my board.
> >>
> >>The flash loader will not keep my external watchdog strobed
> >>and will not be able to avoid a reset as a result. So the
> >>external watchdog will keep it from working.
> >>
> >>Question: Does the phillips flash loader toggle and pin
> >>regularly that I could use for this strobe?
> >>
> >>Can I hook it somehow to make it pet the dog?
> >>
> >>Any ideas?
> >>
> >>Landrum
> >>
> 
> 
> -- 
> /************************************************
>  Do you need a tiny and efficient real time
>  operating system (RTOS) with a preemtive
>  multitasking for LPC2000 or AT91SAM7?
> 
>    http://nanortos.net-attack.de/
> 
>  Or some open-source tools and code for LPC2000?
> 
>    http://www.net-attack.de/
> 
> ************************************************/
>

At 06:29 PM 10/17/05 +0000, lhaddix wrote:
>I think I will add circuitry to inhibit the external watchdog
>when P0.14 is low. I also want to inhibit the external watchdog
>when my 20pin JTAG is in use.
>
>What can I sense to tell if the JTAG port is connected to an
>emulator?
>
>I thought about counting on one of it's many grounds
>pulling a pin low, but would rather use something that didn't
>depend on certain grounds being connected inside the emulator
>pod.

What about using the pin that enables JTAG in the same manner as you are 
planning on using P0.14?  That doesn't detect the cable presence but it 
does detect JTAG on (so to speak)  It would fail if the cable was present 
and JTAG not enabled but then JTAG won't work in that case anyway ....

Robert

" 'Freedom' has no meaning of itself.  There are always restrictions,   be 
they legal, genetic, or physical.  If you don't believe me, try to chew a 
radio signal. "  -- Kelvin Throop, III
http://www.aeolusdevelopment.com/

One thing which will kill your internal Watchdog is writing a large 
value to the WDTC register.  While the WDMOD register is write-
protected, this register is not.

Also, even though WDMOD is protected from writes by the core, could 
static possibly change the setting of one of its bits?

Also, is it possible that static could cause a Reset, and then crash 
the processor before the code has a chance to set the WDEN bit?



--- In lpc2000@yahoogroups.com, "lhaddix" <lhaddix@i...> wrote:

>
> I guess as Marcio points out the larger issue is why are there
> situations where the internal watchdog can't reset the micro.
> Unfortunately this is probably a feature of the LPC design.
> 
> Microchip uses an internal RC for thier watchdog which is not
> dependant of the system clock for instance.
> 
> I think what happens is it's possible for an ESD hit to stop
> the crystal osc on the LPC such that reset is needed to restart
> the oscillator, but there can be no watchdog reset without a system 
> clock.
> 
> I've considered using an external osc to feed the ARM, but don't
> wish to do this. I can't be sure it would fix the problem without
> mocking it up and then blasting with the static gun, but I know that
> toggling reset from outside will restart the clock. 
> 
> Landrum
>

lhaddix wrote:
> Sten,
> What do you mean 'bad foul!!!' my design or this situation?
The situation of course! This is like building a house without a door. ;-)

> 
> I think I will add circuitry to inhibit the external watchdog
> when P0.14 is low. I also want to inhibit the external watchdog
> when my 20pin JTAG is in use. 
> 
> What can I sense to tell if the JTAG port is connected to an 
> emulator? 

Roberts idea with the JTAG-Enable pin (RTCK) is quite good. If you
pull-up this pin (e.g. LPC2138) JTAG is enabled. If this pin is
unconnected (or pulled-low) JTAG will be disabled.

> 
> I thought about counting on one of it's many grounds
> pulling a pin low, but would rather use something that didn't
> depend on certain grounds being connected inside the emulator
> pod.
Mmmmh...

> 
> I guess as Marcio points out the larger issue is why are there
> situations where the internal watchdog can't reset the micro.
> Unfortunately this is probably a feature of the LPC design.
> 
> Microchip uses an internal RC for thier watchdog which is not
> dependant of the system clock for instance.
> 
> I think what happens is it's possible for an ESD hit to stop
> the crystal osc on the LPC such that reset is needed to restart
> the oscillator, but there can be no watchdog reset without a system 
> clock.
> 
> I've considered using an external osc to feed the ARM, but don't
> wish to do this. I can't be sure it would fix the problem without
> mocking it up and then blasting with the static gun, but I know that
> toggling reset from outside will restart the clock. 
> 
> Landrum
> 

I had some similar problems with a LPC2124 last year. During ESD test
the LPC stops with and without internal watchdog. But we had another
(bigger) MCU on our board which was able to turn off/turn on the LPC if
it didn't response to hello-request packet in such a case.

  Sten
-- 
/************************************************
 Do you need a tiny and efficient real time
 operating system (RTOS) with a preemtive
 multitasking for LPC2000 or AT91SAM7?

   http://nanortos.net-attack.de/

 Or some open-source tools and code for LPC2000?

   http://www.net-attack.de/

************************************************/

lhaddix wrote:

>Hi,
>I'm working on an LPC2138 design and just moved
>into ESD testing. After some ESD hits there was
>no damage, but the processor would be left not 
>running.
>
>  
>
I'm wondering why you would subject a board's electronics to a static 
discharge??  When we go through U/L testings, they zap us with an ESD on 
the inputs of the board, but they don't start showering the board with 
static charges.

In our case, it is a matter of going after the source of the problem, 
the EMF wave introduced by the discharge.  I had one design where it 
used an AT style keyboard.  Sometimes when you plugged the keyboard in, 
the 8041 processor would lockup, in that case also, you had to power 
cycle the processor to get it working again.  Our solution had been 
simple, add a couple of silicon (1N4148) diodes to the signal lines in 
question to dump the excess voltage into the power supply bus (low 
impedance).

Other solutions we use is the classic Transorb (gas tube), resistor and 
Transil (high speed zenor).  This works exceptionally well in situations 
where high-voltage may be induced into wiring due to nearby lightning 
storms.

IMHO, you are working towards the solution backwards?  I mean, fixing 
the result rather than the cause?

TomW


-- 
Tom Walsh - WN3L - Embedded Systems Consultant
http://openhardware.net, http://cyberiansoftware.com
"Windows? No thanks, I have work to do..."
----------------------------------------------------

At 12:04 AM 10/18/05 +0200, Sten wrote:
>lhaddix wrote:
> > I guess as Marcio points out the larger issue is why are there
> > situations where the internal watchdog can't reset the micro.
> > Unfortunately this is probably a feature of the LPC design.
> >
> > Microchip uses an internal RC for thier watchdog which is not
> > dependant of the system clock for instance.
> >
> > I think what happens is it's possible for an ESD hit to stop
> > the crystal osc on the LPC such that reset is needed to restart
> > the oscillator, but there can be no watchdog reset without a system
> > clock.
> >
> > I've considered using an external osc to feed the ARM, but don't
> > wish to do this. I can't be sure it would fix the problem without
> > mocking it up and then blasting with the static gun, but I know that
> > toggling reset from outside will restart the clock.
> >
> > Landrum
> >
>
>I had some similar problems with a LPC2124 last year. During ESD test
>the LPC stops with and without internal watchdog. But we had another
>(bigger) MCU on our board which was able to turn off/turn on the LPC if
>it didn't response to hello-request packet in such a case.


I think the additional micro as watchdog is not a bad idea.  A little 8 pin 
micro can act as quit a flexible watchdog.  1 pin for reset, 1 as the 
watchdog input, a couple to check for various startup or runtime 
conditions.  If it has a good reliable power monitor built in even 
better.  It' may even be cost competitive with a windowed watchdog.

Jack Ganselle has an article where he waxes rhapsodic about the possibilities.

Robert

" 'Freedom' has no meaning of itself.  There are always restrictions,   be 
they legal, genetic, or physical.  If you don't believe me, try to chew a 
radio signal. "  -- Kelvin Throop, III
http://www.aeolusdevelopment.com/

I've been using an external 8-pin micro as a reset/watchdog control for 
years. Originally I used the PIC12C509 and more recently the 12C629 as 
they have proved very reliable. Even the LPC903, albeit in SMD. Use the 
internal RC oscillator, apply VDD and presto. The watchdog can be a 
smart watchdog that requires a serial bit stream to start it up and 
continue to activate it or whatever you like.

But I never waste resources as this micro always monitors my main coms 
receive line and allows me to remotely reset, stop, or place the host 
micro in bootload mode. Back in the nineties I was guilty of using AVRs 
which did not have any internal boot code but could be Flash programmed 
via an SPI like interface. So the external reset micro would be kind 
enough to receive an intel hex file and burn it in line by line, all 
over a 3-wire serial interface. Of course, I use them on my LPC2000s as 
well.

One reason I like the 8-pin DIP format is for that reason ... DIP, as 
everything else tends to be smd I can still burn my special watchdog 
chip externally and then plug it in. I even code serial numbers in these 
little suckers. I have yet to make one of these lock-up or even glitch.

There you go, combo reset/watchdog/ISP/serial# chip, all for a buck.

..and yes, I have waxed lyrical about this once or twice before.

my2cents
*Peter*

Robert Adsett wrote:

>At 12:04 AM 10/18/05 +0200, Sten wrote:
>  
>
>>lhaddix wrote:
>>    
>>
>>>I guess as Marcio points out the larger issue is why are there
>>>situations where the internal watchdog can't reset the micro.
>>>Unfortunately this is probably a feature of the LPC design.
>>>
>>>Microchip uses an internal RC for thier watchdog which is not
>>>dependant of the system clock for instance.
>>>
>>>I think what happens is it's possible for an ESD hit to stop
>>>the crystal osc on the LPC such that reset is needed to restart
>>>the oscillator, but there can be no watchdog reset without a system
>>>clock.
>>>
>>>I've considered using an external osc to feed the ARM, but don't
>>>wish to do this. I can't be sure it would fix the problem without
>>>mocking it up and then blasting with the static gun, but I know that
>>>toggling reset from outside will restart the clock.
>>>
>>>Landrum
>>>
>>>      
>>>
>>I had some similar problems with a LPC2124 last year. During ESD test
>>the LPC stops with and without internal watchdog. But we had another
>>(bigger) MCU on our board which was able to turn off/turn on the LPC if
>>it didn't response to hello-request packet in such a case.
>>    
>>
>
>
>I think the additional micro as watchdog is not a bad idea.  A little 8 pin 
>micro can act as quit a flexible watchdog.  1 pin for reset, 1 as the 
>watchdog input, a couple to check for various startup or runtime 
>conditions.  If it has a good reliable power monitor built in even 
>better.  It' may even be cost competitive with a windowed watchdog.
>
>Jack Ganselle has an article where he waxes rhapsodic about the possibilities.
>
>Robert
>  
>

TomW,
We use a gun and step from a couple of KV to +/-25KV.
All of my connector pins pass though these surge devices
we use called SurgX that will clamp the pulse to 30v and turn
on in about 50ps. My connectors can handle being hit directly.

However our board is mounted in a metal frame which they
also shoot with the gun. At first we had the board isolated from
the frame, but the only way out for the pulse is the ground plane
on the board so it flashes over to the board. (As much as 3/4"!!!)

I stopped this by giving the board a low impedance ground to the
frame so the whole thing bounces up and down as quickly as possible.
This prevents component damage, but still apparently leaves gradients
that will freak out the ARM.

We have a four layer board with both outside layers as ground planes.
As well as inner ground polygons poured around the traces.
A ton of vias stitch the grounds planes together as well.

However I'm still thinking we can get a pretty good gradient between
some of the nets when the board takes a hit. (25kv human body model 
is a lot of bang...)

I also run many of the lines after passing through the surgx devices
through BAV99 diode clamps to both rails.

About all I can do is ground all 4 edges of the board rather than just
the single 1/2" copper tape tail the board has soldered to it now.

As I said we can take 25Kv no sweat it just sometimes crashes the
micro.

With a reliable watchdog it would come right back up.


Landrum Haddix
lhaddix@...
http://web.qx.net/lhaddix

> I think the additional micro as watchdog is not a bad idea.  A little 8 pin 
> micro can act as quit a flexible watchdog.  1 pin for reset, 1 as the 
> watchdog input, a couple to check for various startup or runtime 
> conditions.  If it has a good reliable power monitor built in even 
> better.  It' may even be cost competitive with a windowed watchdog.
> 
> Jack Ganselle has an article where he waxes rhapsodic about the possibilities.
> 
> Robert

Robert,
We thought of that today. There are some SOT-23 PICs with 4 I/O that
would be cheap and perfect. Downside is they have to be programmed
somehow. So far my design is entirely flashable from outside.

You could even speak I2C to it and schedule the next reset pulse to
occur if there is no further comm.  This could even include as special
value for the duration that meant disable the watchdog function.

It's dissapointing however to have to use a PIC beacuse it has a 
reliable watchdog and BOR to pull reset on the ARM because it doesn't.

Landrum Haddix
lhaddix@...
http://web.qx.net/lhaddix

Landrum Haddix wrote:

>TomW,
>We use a gun and step from a couple of KV to +/-25KV.
>All of my connector pins pass though these surge devices
>we use called SurgX that will clamp the pulse to 30v and turn
>on in about 50ps. My connectors can handle being hit directly.
>
>  
>
This almost sounds like a High-Energy Laser controller...


>However our board is mounted in a metal frame which they
>also shoot with the gun. At first we had the board isolated from
>the frame, but the only way out for the pulse is the ground plane
>on the board so it flashes over to the board. (As much as 3/4"!!!)
>
>I stopped this by giving the board a low impedance ground to the
>frame so the whole thing bounces up and down as quickly as possible.
>This prevents component damage, but still apparently leaves gradients
>that will freak out the ARM.
>
>  
>
Well, all I can say is that I am glad it is you and not me with this 
problem.  In the field that I do stuff, if we had that much voltage 
dancing around the metal enclosure, it won't matter what the outcome 
would be... heh  We only have to deal with the vulnerability of the 
external connections.


TomW


-- 
Tom Walsh - WN3L - Embedded Systems Consultant
http://openhardware.net, http://cyberiansoftware.com
"Windows? No thanks, I have work to do..."
----------------------------------------------------

At 10:12 PM 10/17/05 -0400, Landrum Haddix wrote:
> > I think the additional micro as watchdog is not a bad idea.  A little 8 
> pin
> > micro can act as quit a flexible watchdog.  1 pin for reset, 1 as the
> > watchdog input, a couple to check for various startup or runtime
> > conditions.  If it has a good reliable power monitor built in even
> > better.  It' may even be cost competitive with a windowed watchdog.
> >
> > Jack Ganselle has an article where he waxes rhapsodic about the 
> possibilities.
> >
> > Robert
>
>Robert,
>We thought of that today. There are some SOT-23 PICs with 4 I/O that
>would be cheap and perfect. Downside is they have to be programmed
>somehow. So far my design is entirely flashable from outside.

Well there is something to be said for having your watchdog be 
non-modifiable :)

>You could even speak I2C to it and schedule the next reset pulse to
>occur if there is no further comm.  This could even include as special
>value for the duration that meant disable the watchdog function.
>
>It's dissapointing however to have to use a PIC beacuse it has a
>reliable watchdog and BOR to pull reset on the ARM because it doesn't.

Well, I've always been too paranoid to rely on a micro to provide a reset 
output in the case of brownout.  A fair power monitor circuit has to 
guarantee a low out (not floating) down to a Vcc of 0.8V, a good one should 
go lower.  Especially important as supply voltages drift ever lower.

One of these days I'll sit down and satisfy myself that it can be made to 
work.  The non power side I'm convinced of.

Which raises a question for the original poster.  Do you have a power 
monitor that provides a reset when your power line goes low.  Pulses on the 
power line could give you the symptoms you see.  And given the environment 
you describe a ground bounce is not out of the question.

Robert

" 'Freedom' has no meaning of itself.  There are always restrictions,   be 
they legal, genetic, or physical.  If you don't believe me, try to chew a 
radio signal. "  -- Kelvin Throop, III
http://www.aeolusdevelopment.com/

Update:

The other day I reported it seemed my LPC2138 was hanging with the
clock stopped and the internal watchdog not working.

Turns out the processor was running so the watchdog was being stroked
hence not firing.

What was happening were I/O lines were changing state after an ESD hit.
In my case this turned off most of my board making it look dead.

Only some I/O lines were flipping, so it's not an easy state to detect.

I've seen this before, I guess it means I need to keep internal copies
of the ports and periodically refresh them. Of course this will only
work for logic that can handle a pin toggling as long as it returns to
the correct state. Something edge triggered would hate this.

Anyhow we solved the ESD problem by metallizing the plastic lid
enclosing the board.

We took 180 consecturive hits at 25kv without crash or reboot.

Pardon my alarm.

Landrum Haddix
lhaddix@...
http://web.qx.net/lhaddix

Landrum Haddix wrote:

>Update:
>
>The other day I reported it seemed my LPC2138 was hanging with the
>clock stopped and the internal watchdog not working.
>
>Turns out the processor was running so the watchdog was being stroked
>hence not firing.
>
>What was happening were I/O lines were changing state after an ESD hit.
>In my case this turned off most of my board making it look dead.
>
>Only some I/O lines were flipping, so it's not an easy state to detect.
>
>I've seen this before, I guess it means I need to keep internal copies
>of the ports and periodically refresh them. Of course this will only
>work for logic that can handle a pin toggling as long as it returns to
>the correct state. Something edge triggered would hate this.
>
>Anyhow we solved the ESD problem by metallizing the plastic lid
>enclosing the board.
>
>  
>
I was going to offer the Faraday Shield as a solution.... heh

TomW


-- 
Tom Walsh - WN3L - Embedded Systems Consultant
http://openhardware.net, http://cyberiansoftware.com
"Windows? No thanks, I have work to do..."
----------------------------------------------------