I'm sharing this for others who are trying to program the AT89S8252 using the SPI interface. I had 2 problems that were not documented in the data sheet or any errata from Atmel. First off, I learned that the SCLK is VERY edge sensitive (Thank you Wagner Lipnharski, who wrote ISPDOS.EXE and did a VERY good job of documenting the problems he found. The web page is http://www.ustr.net/files/download.shtml). If you are having problems, use a Schmit trigger device between the parallel port and the '8252. This will give you a better square wave on the SCLK. I used a 74HCT132 device from Radio Shack. I was using a 74AC244, that part did not work at ALL. After I switched out the 74AC244 I was getting some feedback from the '8252 but I was still unable to program the part. After trying all kinds of tests, I decided to try a different cable. I went out and bought one of those fancy "Gold" plated 25 pin cables and that solved the problem. You could probably do okay with a smaller (less than 6ft) cable or make your own, but 6' was all I could find. I still had some small problems with programming, but by slowing down my timing, I was able to program the part. Wagner Lipnharski mentioned that the Schmit trigger would induce some high frequency noise on the SPI lines and that could be eliminated by using a 1nf cap on the SPI pins. I did not bother trying this because programming speed is not a concern for me. So, if you are having problems with programming the '8252 , try using a schmit trigger device and the best/smallest quality cable you can find. I hope this saves someone out there the hours I spent figuring out my problems.

Best Regards,
Mike Payne
Mpayne@austin.rr.com