piclist 2008\07\10\081651a >
Thread: antistatic protection for PIC burner
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face picon face BY : email (remove spam text)(Olin Lathrop)



Xiaofan Chen wrote:
>> On that part make sure that PGM is held low even though it is not
>> connected to the programmer.  I would just tie it to ground at the
>> socket.
>
> I do not think this is applicable to PIC18F2550. I do not this with
> either PICKit 2 and MPLAB ICD2.

The 18F2550 definitely has a PGM pin.  On some PICs, including some 18F,
programming may fail if PGM is raised at the wrong time and LVP is enabled.
Apparently, raising MCLR to the programming voltage doesn't always enter
programming mode correctly if PGM was active and previously raised.  I have
seen this problem, including on a 16F628 and I think a 18F252 (suspected but
couldn't prove it).  I don't know for sure that the 18F2550 is immune to
this problem, so I assume it's not.

Note that LVP is implicitly enabled by a bulk erase, which many programmers
will do before trying to write the HEX file data to the target.  This means
LVP is enabled during most of the programming operation, even if it is
disabled in your code.

You can get away with it much of the time, but I make sure PGM is held low
during programming.  The OP asked about wiring up a socket adapter for a
in-circuit programmer, so this is just a matter of a wire between PGM and
Vss.  It seems like a no-brainer to me to install the wire.  I have on all
my programming adapters.


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