Stephen Webb wrote:
>
> > Do the chips get hot if VPP is isolated?
>
> I'm not sure what you mean by this.

Just trying to ascertain if VPP is causing the problem or VCC.

If you isolate VPP then 13V will not appear on MCLR.

You won't be able to program this way, but you will be able to read data
although it will probably be all 0000's.

The idea is to check the chip temperature while you do these dummy reads
without 13V VPP applied. If the chip stays cool, it's most likely the
VCC voltage causing the problem.

Another thing - are RB6 and RB7 both low when MCLR is raised to VPP.
This must occur for the chip to enter programming mode.

As another simple test, you can tie RB6/7 to GND, apply 5V while MCLR is
tied low via a 22K resistor. See if the chip gets hot after awhile. If
it does, I would say the chip is faulty.

If not, apply 12~13V to MCLR and now see if the chip gets hot. Better
yet, use a multimeter to measure the current going into MCLR. It should
be in the order of microamps. If you measure a high current which would
be causing the heating, then the chip is faulty.

If the high voltage caused the problem, then the chips are most likely
dead by now anyway.


--
Best regards

Tony

mICros
http://www.bubblesoftonline.com
mailto:sales@bubblesoftonline.com

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