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
WWW WWW Adrian Gothard
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Developers of GPS satellite-based tracking systems for vehicles/helicopters
> 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.
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.
>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
>
>WWW WWW Adrian Gothard
>WWW WW WWW White Horse Design
>WWWWWWWWWW +44-385-970009 (Mobile/SMS), +44-118-962-8913/4 (voice/fax)
>WWWW WWWW .....whdKILLspam@spam@zetnet.co.uk,http://www.users.zetnet.co.uk/whd
>---
>Developers of GPS satellite-based tracking systems for vehicles/helicopters
>
>
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?
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!
>>> 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.
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
WWW WWW Adrian Gothard
WWW WW WWW White Horse Design
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---
Developers of GPS satellite-based tracking systems for vehicles/helicopters
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
WWW WWW Adrian Gothard
WWW WW WWW White Horse Design
WWWWWWWWWW +44-385-970009 (Mobile/SMS), +44-118-962-8913/4 (voice/fax)
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---
Developers of GPS satellite-based tracking systems for vehicles/helicopters
>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
==================================================================
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
>==================================================================
>
>>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
==================================================================
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}
>>> 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
>
>WWW WWW Adrian Gothard
>WWW WW WWW White Horse Design
>WWWWWWWWWW +44-385-970009 (Mobile/SMS), +44-118-962-8913/4 (voice/fax)
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>---
>Developers of GPS satellite-based tracking systems for vehicles/helicopters
>
>
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