> One interesting thing with the charge pump in this design is
> that it is
> generated by hardware  alone, not software.

One problem I have experienced with my WISP/Wisp628 that use the same
principle is that the Vpp level is directly releated to the Vcc level.
When the Vcc is too low (for instance 4.5 Volt) some PICs (older ones,
mainly 16c84, 16F84) won't go into programming mode. IIRC the minimum
voltage level on USB is way lower than 5.0 Volt. Don't you expect
trouble from this?

Wouter van Ooijen

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Van Ooijen Technische Informatica: www.voti.nl
consultancy, development, PICmicro products

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