Rustu,

I recently switched from AT89C52 to AT89C55WD. I also faced such problems, but these were due to ALE.


In AT89C52, if you leave EA floating, the chip works from internal code memory (perhaps there is some internal pull-up) but AT89C55WD does require a pull up on EA.

AT89C55WD does not work (or strange behaviour) if EA is pulled with a high resistance e.g. 100K does not work. 10K is good.

ATMEL advised me to change RESET circuit, but my experience is that same (10K+10uF) works fine on WD as well.


Good Luck

IA