On Thu, 23 Sep 2004 16:33:47 +0100, you wrote:

>>
>> I'm not sure it applies to this part, but I know the 12F parts
>> are sensitive to Vcc risetime, which
>> can cause problems when there is capacitance or other loading on
>> the supply.
>>
>
>Thank you for the tip Mike. I've checked this with power from the ICD2 - It
>takes 15us for the Vcc pin to reach 2V, and a further 80us to reach 4.5V.
>
>When I use power from the board instead, the waveform of the rise of Vcc is
>much more drawn out - Vcc takes 1ms to reach 1.4V, then climbs quicker to
>2.6V in a further 40us, and then slowly again to 3.3V (full voltage in this
>configuration) in a further 2.5ms. Maybe this is due to characteristics of
>the bench power supply.
>
>Could these kind of risetimes for Vcc be significant with the
>erasing/reprogramming problems? Whichever source of power the trouble is the
>same.

When I was looking at the 12f's, ISTR the main problem was that Picstart was not leaving enough
delay between Vcc and Vpp - it was not so much the risetime as the delay - potentially tweakable in
software, if you can get at the software.... 

For a producton programming jig I did a while ago I used the PP06 programmer software which comes
with source code - I didn't get as far as looking at this as I had to build the hardware anyway so
made it suitable beefy - I just wanted to get the programming time down to a minimum.

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