Kovalenko Alexander wrote:

AT89S52 has several new registers (AUXR, AUXR1, WDTRST, DP1L, DP1H) in comparison with AT89C52. Maybe I should do additional initialisation of these registers? Also there are a lot of variables in RAM. Is it possible, that some variable changes value of these new registers?

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Dear Kovalenko , You know the reason ? .If you are using some '51 compiler do you include proper data file ? or header file that corresponds to 89s52 and not 89c52 before compiling ? and if you are using Assembly you need to change the registers if they are assigned a different address for different derivative .

hope this helps
Sanjeev