Robin Abbott wrote:
> Wouter's email gave me pause for thought. On all of our PIC applications we
> have left unused pins to float and normally set to input without any
> apparent ill effect. However in the old days of CMOS this was bad news as
> the high impedance could lead to oscillating inputs and high current drain. 
>
> Does anyone know if this applies to PIC's or has the input technology long
> moved on?
>
> Robin Abbott
> Forest Electronics - Home of WIZ-C ANSI C Compiler for PIC's with RAD Front
> end
> robin.abbott@fored.co.uk
> www.fored.co.uk 
>  
>
> -----Original Message-----
> From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On Behalf Of
> wouter van ooijen
> Sent: 16 November 2007 22:39
> To: 'Microcontroller discussion list - Public.'
> Subject: RE: [PIC] PIC looses it's program memory
>
>   
>> I just checked I have 2 open inputs. How can open input change program 
>> memory?
>>     
>
> Dunno, but open inputs can be bad: just a little charge can create an
> out-of-spec volatage on the pins. And the trouble with out-of-spec is that
> it is out-of-spec, that is: behaviour is not guaranteed. 
>
> Wouter van Ooijen
>
> -- -------------------------------------------
> Van Ooijen Technische Informatica: www.voti.nl consultancy, development,
> PICmicro products docent Hogeschool van Utrecht: www.voti.nl/hvu
>  
>  
>
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>   
Unused pins are always set to outputs, and held low, in my designs, 
except when they are used for
debugging during development.

Never ever had an issue like this; but my guess is that the MCLR line is 
being spiked, and it is somehow
entering programming mode. That is one drawback to the use of the MCLR 
line for purposes other than
programming. I seriously doubt that self-programming mode could be the 
cause; the "magic process" makes
accidental writes literally impossible (h'AA' to eecon1, h'55' to 
eecon1, then write command).

--Bob A
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