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PICList Thread
'PIC16C74 fails, 74A succeeds (automotive)'
1998\07\15@151140 by White Horse Design

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We've found that a JW (EPROM 20MHz) PIC device fails when powered up in the
car. It is directly connected to 12V with some minor protection (transil I
think was added by the designer of the "other" main board).

When a 74A (3.6864MHz crystal both times) is substituted it works ok. He
tried turning the engine on and off 10 times successfully for the 74A device.

Failure is total system lockup at power up.

The circuit is controlled by a MAX691A controlling the RESET\ line (default
is a *long* delay 1.5 seconds from memory). We blew the same code into both
devices (without brown-out enable on the 74A). The unit is in the car so no
extremes of temperature.

I suspect a power problem but the other designer wouldn't put on the
filters (in power *and* ground) that I wanted.

As far as I know the 74A only has the brown-out and a higher temperature
specification??

Regards

Adrian

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Developers of GPS satellite-based tracking systems for vehicles/helicopters

1998\07\15@154100 by Bob Blick

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On Wed, 15 Jul 1998, White Horse Design wrote:

> We've found that a JW (EPROM 20MHz) PIC device fails when powered up in the
> car. It is directly connected to 12V with some minor protection

I'm surprised any of them survived at all. I've had bad luck past about 8
volts. You really need a regulator or something to drop the 12 volts down.

Cheers,
Bob

1998\07\15@171414 by Matt Bonner

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> We've found that a JW (EPROM 20MHz) PIC device fails when powered up in the
> car. It is directly connected to 12V with some minor protection (transil I
> think was added by the designer of the "other" main board).

You're running it _way_ out of spec at 12V.
>
> When a 74A (3.6864MHz crystal both times) is substituted it works ok.

But how long will it work?  You're still running it out of spec, just
not as fast.  There are lots of low-quiescent, low drop-out 3 terminal
regulators.

> As far as I know the 74A only has the brown-out and a higher temperature
> specification??
>
Brown-out, yes; higher temp, no.  I think the BRGH silicon bug was fixed
on the '74A.

--Matt

1998\07\15@173220 by Peter Grey

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At 08:05 PM 15/07/98 +0100, you wrote:

Adrian,
A few years ago I had a real problem with 74 resetting due to noise in an
analyser we were building. It had a number of motors running and although we
could see nothing on a scope it kept happening. We put a lot of nosie
suppression caps, filters around and eventually it was solved by caps across
two hobby motors. A comment was made by my colleagues that the 74 was very
intolerant of noise and reallly needs to be designed for. I have not tried a
74A in teh same design but will do so when I get the opportunity.

Regards,

Peter
Neosystems
Australia

{Quote hidden}

1998\07\16@040912 by Jim robertson

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At 14:54 15/07/98 -0600, you wrote:
>> We've found that a JW (EPROM 20MHz) PIC device fails when powered up in the
>> car. It is directly connected to 12V with some minor protection (transil I
>> think was added by the designer of the "other" main board).
>
>You're running it _way_ out of spec at 12V.
>>
>> When a 74A (3.6864MHz crystal both times) is substituted it works ok.
>
>But how long will it work?  You're still running it out of spec, just
>not as fast.  There are lots of low-quiescent, low drop-out 3 terminal
>regulators.
>
>> As far as I know the 74A only has the brown-out and a higher temperature
>> specification??
>>
>Brown-out, yes; higher temp, no.  I think the BRGH silicon bug was fixed
>on the '74A.

No, I believe it wasn't. It was first fixed on the 8K parts and possibly
retro-fitted  on later A revisions but you cannot assume that all A
revisions have the bug fixed.

BTW The Non-A 16C74s actually have got a brownout reset circuit fitted. IT
is not documented or tested and normally disabled during programming as the
programming spec specifies Bit-6, the brownout bit, be programmed as a '0'

If the programmer does not do this then who knows what the results might be?

Jim

>--Matt
>

1998\07\16@044510 by White Horse Design

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At 18:13 16/07/98 +1000, you wrote:
>At 14:54 15/07/98 -0600, you wrote:
>>> We've found that a JW (EPROM 20MHz) PIC device fails when powered up in
the
>>> car. It is directly connected to 12V with some minor protection (transil I
>>> think was added by the designer of the "other" main board).
>>
>>You're running it _way_ out of spec at 12V.

Sorry, should have said through a 7805, but otherwise directly connected!

{Quote hidden}

Correct as I understand it.
That's why I'm using a 3.6864MHz crystal for perfect 4800 and 9600 baud rates.

>BTW The Non-A 16C74s actually have got a brownout reset circuit fitted. IT
>is not documented or tested and normally disabled during programming as the
>programming spec specifies Bit-6, the brownout bit, be programmed as a '0'
>
>If the programmer does not do this then who knows what the results might be?

We didn't program the BOR bits at all.

Regards

Adrian

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Developers of GPS satellite-based tracking systems for vehicles/helicopters

1998\07\16@044518 by White Horse Design

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At 12:28 15/07/98 -0700, you wrote:
>On Wed, 15 Jul 1998, White Horse Design wrote:
>
>> We've found that a JW (EPROM 20MHz) PIC device fails when powered up in the
>> car. It is directly connected to 12V with some minor protection
>
>I'm surprised any of them survived at all. I've had bad luck past about 8
>volts. You really need a regulator or something to drop the 12 volts down.

Sorry should have said I'm using a 7805!

(By "directly" I meant we are not using a dc-dc (isolated) converter module
such as the Alphatronnix which we do use on the lorry systems (24 down to
12V))

Regards

Adrian

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Developers of GPS satellite-based tracking systems for vehicles/helicopters

1998\07\16@104513 by Andy Kunz

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>No, I believe it wasn't. It was first fixed on the 8K parts and possibly
>retro-fitted  on later A revisions but you cannot assume that all A
>revisions have the bug fixed.

I was told by an FAE that we have to wait for "B" parts on the 4K parts.

Andy

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

1998\07\16@230720 by Jim robertson

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At 10:11 16/07/98 -0400, you wrote:
>>No, I believe it wasn't. It was first fixed on the 8K parts and possibly
>>retro-fitted  on later A revisions but you cannot assume that all A
>>revisions have the bug fixed.
>
>I was told by an FAE that we have to wait for "B" parts on the 4K parts.
>
>Andy

Yer, that sounds right. There is a 16C62B either available now or very
shortly.  Not sure about the wait on other parts.

Jim

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

1998\07\17@085941 by Andy Kunz

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>>I was told by an FAE that we have to wait for "B" parts on the 4K parts.
>>
>Yer, that sounds right. There is a 16C62B either available now or very
>shortly.  Not sure about the wait on other parts.

They're all the same die, so they should come out together.

Andy


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

1998\07\19@133248 by Larry G. Nelson Sr.

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In automotive systems there's a tremendous amount of electrical noise.  The
automotive specifications allow for very high voltage spikes and surges.  I
designed a system for use on transit buses in Europe.  When the air
conditioner cycle there were voltage surges in excess of 100 volts.  When
the brakes were applied and released there were also electrical surges. The
input voltage rating on a 7805 regulator is lower than the noise you are
likely to see.  Minimally you should put filtering and some means of spike
protection on the input to the regulator.  Instead of the 7805 you may want
to consider using a switch mode controller such as one of the simple
switcher chips.



At 09:41 AM 7/16/98 +0100, you wrote:
>At 12:28 15/07/98 -0700, you wrote:
>>On Wed, 15 Jul 1998, White Horse Design wrote:
>>
>>> We've found that a JW (EPROM 20MHz) PIC device fails when powered up in
the
{Quote hidden}

Larry G. Nelson Sr.
L.Nelsonspamspam_OUTieee.org
http://www.ultranet.com/~nr

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