On Wed, Apr 30, 2003 at 01:51:39PM -0500, Picdude wrote:
> Well I tried this, but still no dice.
>
> I found the reference to this in the datasheet -- DS30221B, pg 102, section
> 11.18.  Says "Note 1:  The High Voltage Programming mode is always available,
> regardless of the state of the LVP bit, by applying Vihh to the !MCLR pin."

The errata of various chip versions have described the problem. What's stated
above is what is supposed to happen. However it isn't reality.

>
> If it's a bug, then it still doesn't work on mine when I forced LVP low, and
> I've used about a dozen 16F872's to date w/o the problem.  More importantly,
> if this is a bug, it seems like this would affect ICSP as well, so what
> happens when/if I want to program a chip in-circuit, and the LVP pin is being
> used for something else?  This may be a problem.

The pin doesn't have to be tied directly to ground. Most folks suggest using
a pulldown resistor in the 10K range. Enough that the pin won't float, not
enough to really affect any meaningful I/O operation.

Since I almost always use LVP mode for programming, I'm used to pulling it down
out of habit.

>
> Will pick up the regulators now and complete my PCB-version, so I can reduce
> variables for debugging this problem.

I hope that your PCB incorporates the LVP pulldown. It will have you some
headaches down the road.

BAJ
>
> Cheers,
> -Neil.
>
>
>
> On Wednesday 30 April 2003 04:29, Michael Rigby-Jones scribbled:
> > Yes, the LVP pin should always be pulled low when programming.  LVP enabled
> > PICs come set for LVP operation from the factory, if this line floats high
> > enough the PIC will enter the programming state at inoportune moments.
> > Some people have never encountered this, but I have definately had it
> > happen to me.
> >
> > Mike
> >
>
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