Hi Kai,

Because of the internal pull-up resistors P3.6 and P3.7 are high even if not connected to +5V.

On the other hand the outputs must never be tied to Vcc directly or the internal sink transistor might be damaged if the output happens to be low. They have to be connected when necessary with a resistor (1K to 10K for example).

All the ICs I checked are new ones. Do you mean by fresh an erased one? In that case, it HAS to output all 1's.

I am almost sure that reading AT89S51 is not a static procedure as described in Atmel datasheet, though AT89C51 is!

Kerim