Hi Kai,

I am just trying to first read AT89S51 before programming it. And as you know, the read mode is rather static since all pins are steady (except XTL1/2). Therefore there is no critical timing requirements.

On the other hand, it is also not a damaged one since my dear DOS programmer (EMP-20) can read it correctly while thinking it is 89C51!

By the way, due to the incompatibilty of the programming pulse of AT89S51 and AT89C51, my old DOS programmer can only program a blank AT89S51 then read/verify it but cannot erase and lock it. So I got the idea to update my stand-alone programmer to accept also 89S51 instead of buying another programmer (I think EMP-20 is rather obsolete now for upgrading).


After designing hundreds of circuits using MCUs, this is the first time I feel really lost!
Did Atmel miss something to mention in their datasheet of AT89S51? Or it is just me... :)

You can ask me to check and test anything that comes to your mind and I will do it although I went through ALL possibilities. I think of it even at bed :))

Kerim