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'In circuit prog 16C84'
1996\08\12@001512 by DOM ALTAMURO

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Want to program a 16C84 when it is in circuit.

Took a look at Micromint PICSTIC schematic to see
how they did it, and it mostly makes sense to me.

Programmer needs access to
RB7 Data
RB6 Clock
Vdd 5V
Vss Gnd
MCLR reset/programming voltage

For MCLR, microchip recommends a diode to 5V to prevent
the programming voltage from getting onto the 5V line.

The PICSTIC has a 4.7K resistor as well as a diode
going from 5V to MCLR.

I am wondering why the 4.7K resistor.
I assume the talent at Micromint didn't just put it in
for the heck of it--i.e. there's a reason why it is there. :-)

But what is the reason?
---
~ SLMR 2.1a ~ `PENTIUM' gets teeth their whitest!!!

1996\08\12@004706 by Steve Hardy

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> From: DOM ALTAMURO <spam_OUTdom.altamuroTakeThisOuTspamconsultant.com>
>
> Want to program a 16C84 when it is in circuit.
> [cut]
>
> The PICSTIC has a 4.7K resistor as well as a diode
> going from 5V to MCLR.
>
> I am wondering why the 4.7K resistor.
> I assume the talent at Micromint didn't just put it in
> for the heck of it--i.e. there's a reason why it is there. :-)
>
> But what is the reason?
> ---
>  ~ SLMR 2.1a ~ `PENTIUM' gets teeth their whitest!!!
>

Speaking from a position of ignorance on the PICSTIC, I would guess
the resistor is there so you can implement a reset by simple switch
of MCLR to ground.  Otherwise, the reset switch may try to pull VDD
to ground (or blow up the diode trying).

Regards,
SJH
Canberra, Australia

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