>  >> I have a PIC16F84 running with its MCLR pin wired to VDD (+5V). If I
>  >> wire it to VPP (+12V), it doesn't stop. Is it normal???
>  >>     Brusque

>  DIB> I think yes. I vaguely recall the checking for VPP happens somehow at
>  DIB> power-up (that's why the minimal increase speed for VPP has been
>  DIB> specified).
>
>  DIB> Imre

> Yupp ... MCLR must be at programming level before the uC's core is
>  (fully) powered up.
>
>  -DS

Well..... if you were talking about PIC12C50x or something similiar I would
agree with you, but the PIC16F84 is really another story!
To get a PIC16F8x into programming mode, two points are important:
1) Set RB6 and RB7 low
2) Raise /MCLR from 0V to +12V fast enough
It is from no importance when the PIC has been powered up. Whenever one of
the pins RB6 or RB7 is not low while raising /MCLR, the PIC will start
running mode as if there were only +5V at /MCLR.
I know this because I used this behaviour on my selfmade prototype programmer
.It has no automatic 5V - 12V switch for programming voltage, so when I'm
bored of switching the manual switch, I just let it in 12V position, but
raise RB6/RB7 to passive high just before I raise /MCLR - this worked for me
(but I don't think microchip recommends it...).
What Imre and DS stated is true for the 12C family, because this devices
share the /MCLR pin with other function (and it might be true for other PICs
than the PC16F8x).

       Florian

P.S.: I'm just starting to hate the AOL-programm, it crashed when I wrote the
first try of this eMail (and it did not crash the first time...).