Many thanks for all who help me in the difficult task of
"16C84 In situ programming". I make a little summary for
all the people who have same problem.

Solution seems to be:
        - connect VCC to the programmer, don't forget to power off the
board first,
        - connect crystal pin to the ground.
        - verify the programming option by reading the chip after
program and verify step to be sure the good oscillator, WDT and so on
are really programmed.

-------------------------
Adolfo Cobo wrote:

> May tbe the Parallax Programmer works in a simmilar way (I dont'k know), then
>you need a programmer with its own power supply (just what I'm trying to
>build now ).

Yes, this is the second thing I do: disconnect the board power supply and
connect VCC pin to the programmer.


Andy Kunz wrote:

>I used the schematic Microchip had in the data sheet with the Parallax
>programmer, and it works very well.  Perhaps you have RB6 and RB7 in
>contention with another device on your target board?

No there is only 4K7 resitor connected to a 2N2222

>Try disconnecting the crystal while programming, the device don't need it.
>It worked for me and the 16C74. I don't know about the 16C84 but it may work
>for you too.  Bonne chance.

Merci beaucoup !

Do you think if I connect the Crystal input to the ground the 84 will
be programmed properly ?
In fact I program the 84 first into the programmer and need now to modify
the program directly on the board.
Then I connect 5 wires from the PCB to the programmer:
        - RB6
        - RB7
        - MCLR
        - VCC
        - GND
Because I cannot un-sold the SMD !

Michael N. Steen wrote:

>Try disconnecting the crystal while programming, the device don't need it.
>It worked for me and the 16C74. I don't know about the 16C84 but it may work
>for you too.  Bonne chance.

Ok I will try it.

Best regards,
        Philippe.