I have a printer port PIC16C84 programmer that I built exactly according
to David Taits' schematic:
http://www.man.ac.uk/~mbhstdj/files/pp.gif

Using his PP software (rev 0.4), I have never had a problem programming
a 'C84 in circuit. Once, an assembly firm switched vendors and a batch
of 1200 surface mount 16C84's were programmed with the wrong OSC fuse
settings. The assembler neglected to inform me of the vendor change, but
did not hesitate to call when none of the boards worked. My 'PP'
programmer saved the day.

So... this same contract assy house decided to switch to 16F84's (yep
same board!). They have so far built about 1500 using F84's, of which
only 400 remain to be shipped. Luckily for them, there has been no
problems due to the chip change this time. My problem is my client
requested a minor (but important) code tweak. The client will not accept
the 400 boards as is. No sweat, I thought. I'd just whip out my trusty
'PP' programmer and save the day, again.

I downloaded rev 0.5 of David Taits' software which supports the F84.

Here's my problem. The 16F84's program just fine, but cannot be read by
the PP. I verified correct programming by desoldering the 'F84 and using
a PICStart Plus. I carefully checked the PP wiring, but it appears fine,
and the debug functions of the PP software work as expected. Not being
able to read the chip means no verify. The boards are to be retested,
but this test will not be able to tell the difference beteen the new and
old PIC code. I could devise a new test, but the difference is only
detectable after about 20 minutes of run time. Not an option.

Has any one else had difficulties reading a 16F84 using the PP
programmer? Not verifying the programming would feel like driving down a
freeway with my eyes closed. I don't want to take the chance.

Dave Sorlien