First I should say that I am not an expert on hardware. I was the one asking questions and being helped in the previous AT89S8252 ISP thread. This means that if anyone sees an error in my answers I hope they will correct me.

1. The schematic states that you should be using HC parts (at the bottom of the schematic) but the schematic itself suggests you are using LS parts. Which are you using? You should be using HC or HCT parts for your connection to the parallel port.

2. I'm not sure what that 1000pF capacitor between parallel port pin 10 and ground is doing. Mine has no such capacitor and instead has a 220 ohm resistor in series on that line. That other 1000pF capacitor between the two inverters on the parallel port pin 8 line doesn't make sense to me either.

3. What's the purpose of all those double '14 inverters? You have I/O lines coming in from (and going out to) the parallel port and then going through an '14 and then through another '14. Perhaps someone can explain that to me but it seems like you could just lose the '14 and end up with the same result.

4. For what it's worth I tried building the programmer using a 74HCT125 (same as '126 but output enable is active low, I couldn't find a '126 locally so I inverted the signal and fed it to the '125). It didn't work for me either. So I switched to a 74HCT541 and it worked fine. I'm not sure whether that was due to some kind of error on my part or if there's some reason why the '125 wouldn't do the job.

Hope that helps. And I also hope that if I any of my answers are wrong that someone else will correct me.

Regards,
Craig Steiner