Jon,
VDD is not the programming voltage pin; MCLR is, a 5 pin connector is
required.
Regards,
Graham Daniel

Jon Hylands wrote:
>
> Hello all,
>
> I have decided in my application to use half a dozen 16F84's to interface
> to a bunch of components.
>
> However, space is very limited, so I want to use the surface-mount version
> of the chip. I plan on programming them in circuit, and will provide a
> four-pin header for each chip on the board. I plan on using RB6 & RB7 only
> for programming, and so will not need to isolate them from the circuit
> (since they will only go to the pins on the header).
>
> The question is, how do I isolate Vdd? I was thinking along the lines of
> running a trace from the Vdd pin directly to the power header pin, and to
> the rest of the circuit through a diode. The diode would be mounted to
> allow current to pass into the chip from the circuit power supply, but not
> from the chip to the rest of the circuit when powered from the programmer.
> Presumably, since the voltage drop would be about 0.6 volts, the power
> running into the PIC from the 5 volt circuit supply would end up being 4.4
> volts,  which is well within the limits.
>
> Will this work? Is there a better way?
>
> Thanks in advance...
>
> Later,
> Jon
>
> --------------------------------------------------------------
>    Jon Hylands      Jon@huv.com      http://www.huv.com/jon
>
>   Project: Micro Seeker (Micro Autonomous Underwater Vehicle)
>            http://www.huv.com