> Walter,
>         I have written a PIC programming program in C to work with a home
> made PIC programmer.  The programmer I built is similar to several
> described in magazines like Nuts & Volts, and Electronics Now.  The
> difference is that mine provides pins to set Vdd to the Max and Min
> voltages for testing (the book said to do this when programming).  Most
> kits don't provide for this, but I find it makes a difference (testing at
> Vdd Min (4.0V) shows if the chip has really been erased).  My program
> talks to the programmer through the parallel printer port.

The programmer I designed has a somewhat similar feature, but I implemented
it a little bit differently: I have two power modes:

[1] Low-power; current-limitted to about 15mA [total]
[2] High-power; current-limitted to about 150mA [total]

There is also a load pot across VDD.  By adjusting this pot, 15mA may made
to yield any voltage from about 2V to about 4.5V.

Then, when I'm going to program, I start out by setting the device to "low
power" and do an "anything there" check.  If nothing is there, the programmer
shuts down immediately.  Otherwise, it does a blank check.  If that passes,
then it turns on "high power", programs the chip, switches to "low power",
and verifies it.  Finally (if needed) it switches to high-power again and
burns the config fuses.

On the occasions where I have incorrectly inserted a part (or ISP cable)
the current limittng and automatic shutdown have been real life-savers.
Those features weren't hard to add, but they have saved me from slagging
a few chips.
and should IMHO be a part of any "serious" programmer.