Seems someone is always wanting to know about Do It Yourself Programmers
for the 16F84. Among the many out there, I decided to build Steve
Marchant's http://www.cam.org/~estdeni/c84soft.html. There is both WIN95
and DOS SW available for this design.

This is to just to pass on the word that the circuit has worked fine for
me for 10 programming cycles of a 16F84 so far.

If you decide to build it:

1) Make sure that you verify that the 555 is operating at or near
250Khz. The 555 that I grabbed out of the junk box would only go to
100Khz so I replaced it with an available 1Mhz oscillator and 74LS74.

2) Be sure to install CX, a .001uF capacitor between pin 12 (programming
clk) and ground even if your target device is located right on the
programmer. This was the last fix I had to make to get it to work and
removing this part (twice) as a test caused it to fail in my circuit.

3) Don't skimp on bypass caps!

4) I decided to use an LM317 adjustable between 12 and 14 volts for the
Vhh circuit. I think Steve's diagram only showed a 12 volt regulator. I
think this is the lower limit recommended, so I adjust mine for about 13
volts.

The DOS version uses the __CONFIG and ID directives, so if you use the
16F84.inc file from MPASM and set these appropriately, the Power up
Timer will be programmed correcly, but will show up reversed in the
verify cycle. The Config Location does not verify as it should (3FF1 in
my case). I will be in contact with Steve to find out what is really
going on. I suspect this is really OK. Does anyone have a clue what
might be happening?

Good Luck