> The idea consist to use the charge pump of the +12 Volt of the MAX 232 to
> sink voltage and current to use for programming the 16F84 when only five
> volt are present.


I hope you mean source, and not sink.. Charge pumps don't sink current.

That said, I have no idea how well regulated that output is, or how
dependent it is on what's connected to the serial outputs.  I've used
the + and - outputs to power op-amps, and actually it works quite well,
but opamps dont' care much about supply voltage. 1V of ripple, and a
couple of volts of uncertanity wouldn't bother my designs at all. I
suspect the VPP spec for the 84 is a bit tighter than that.

You might find that it goes high enough to use a 78L12 to regulate it, I
wouldn't suggest a zener, that would cause the charge pump to work
overtime. (The zener draws more current with higher input, the linear
draws same current.)