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'[PIC] LVP, bulk erase and potential problems (and '
2005\11\29@082232 by Jan-Erik Soderholm

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Hi.
Now, if I have understood things correctly, there is
a potential problem during bulk erase with the LVP
feature. A bulk erase will reset the LVP bit and enable
LVP. If the programmer then releases the target PIC
from programming mode (by lowering the prog
voltage on MCLR), there is a risk that the
processor will enter LVP mode (if the PGM pin
isn't pulled down with a resistor.

And (still if I've understood correctly), this is
not a problem if the programmer keeps the MCLR
pin at Vpp over the whole erase to fuse re-programming
cycle (?).

And also that a pulldown on the PGM pin will
always protect against this scenario ?

The reason I ask is that the Wisp628 has a
LVP connection/cable. I've never connected
it to anything myself, and it's not perfectly clear
from Wouters Wisp628 page *when* it should
be used. I'd like to understand the LVP issues
fully to be able to better support my local
Wisp628 customers in Sweden.

On a local Swedish electronics forum, there was a
statement today saying that failing to handle the PGM
pin correctly can brake a 16F628A. Comments ?

Best Regards,
Jan-Erik.




2005\11\29@083749 by Michael Rigby-Jones

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{Quote hidden}

Putting a pulldown on the PGM pin should prevent any programming issues.  The only time LVP has ever given me grief was when it was accidently left floating.

Regards

Mike

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2005\11\29@084557 by olin piclist

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Jan-Erik Soderholm wrote:
> And (still if I've understood correctly), this is
> not a problem if the programmer keeps the MCLR
> pin at Vpp over the whole erase to fuse re-programming
> cycle (?).

Yes, if it can.  Note that Vpp is often required to go to 0 between some
operations, like bulk erase and programming data.

> And also that a pulldown on the PGM pin will
> always protect against this scenario ?

Yes.

> On a local Swedish electronics forum, there was a
> statement today saying that failing to handle the PGM
> pin correctly can brake a 16F628A.

Maybe, but I would need to see solid evidence for me to believe that.


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consultant in 2004 program year.  http://www.embedinc.com/products

2005\11\29@174533 by Wouter van Ooijen

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[yes! a PIC topic!]

> The reason I ask is that the Wisp628 has a
> LVP connection/cable. I've never connected
> it to anything myself, and it's not perfectly clear
> from Wouters Wisp628 page *when* it should
> be used.

I don't realy know when it could be *unconnected* so I always connect it
to the PGM pin (that is, if the chip has one).

> On a local Swedish electronics forum, there was a
> statement today saying that failing to handle the PGM
> pin correctly can brake a 16F628A. Comments ?

break the chip? I would be surprised!

Wouter van Ooijen

-- -------------------------------------------
Van Ooijen Technische Informatica: http://www.voti.nl
consultancy, development, PICmicro products
docent Hogeschool van Utrecht: http://www.voti.nl/hvu


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