Mike Hackshaw wrote:

> ...I wonder if you have a series resistor in the line driving the Vpp pin?
>
> ...Another thing I would have looked at would have been the rise times of
the
> Vdd and Vpp supplies...


Hi Mike,

The only catch is the 'size' of this resistance: you want to keep the Vpp
source impedance (and the impedance of its switching circuitry) as low as
possible if you want to conform to any of the Microchip programming
specifications that dictate a Vpp rise time of < 1 uS.

It does not take much Vpp source impedance coupled with any external
capacitance a user may have on the target PIC's Vpp pin to violate this part
of the specification.

The Microchip ICD 2 uses a Vishay/Siliconix DG411DY quad SPST CMOS analog
switch for Vpp switching. I would venture to guess that they are paralleling
a few of the switches to lower the Rds ON of the 'composite' Vpp switch to
help in this regard.

Best regards,

Ken Pergola

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