>But how can you change ALE signal ? I dont get >you ,what exactly are you trying to do?.

I do not change ALE signal. I can see that ALE pin is changing when I use oscillograph. My program must work with LCD (P1.2 - P1.4 pins), I2C bus (P2.0 - P2.4 pins) and RS485 (P3.6 pin). When I use oscillograph I can see that all these pins have high level and do not change.
Also I wrote a small test program, which just counts seconds, writes values of seconds to I2C bus memory, to RS485, and to LCD. And it works on AT89S52...
In my real program there is a lot of variables in RAM. Maybe some variable changes value of some new special register in AT89S52?