Hi
I have used a 5pin header for in circuit programming .
I have used the blocking diode configuration for all five programming pins and
it seems to work  ok.
I only program when the power to the target board is disconnected.
ASH - UK -

on 28 Apr 98, g.daniel.invent.design@xtra.co.nz wrote...

>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
>
>