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We're using AT89C51ED2, and now are busy with a problem, witch was caused by reading back the content of XRAM. As it is officially published in datasheet, this MC has 1792 bytes of internal XRAM. We have set the XRS's bits for selecting the full size of XRAM, and cleared the EXTRAM bit, and EEE bit, mapping the XRAM segment. After that, we are writing data to XRAM using MOVX @DPTR, A procedure. After we have reashed the last adress we are trying to readback the data from XRAM and it is not correct at all.
hi, It is true, that Atmel suggests not to use the R0 registers for accessing the XRAM larger then FFh, but nobody says that it should not work. You should read the datasheet once again. Thay do say that it does not work: ===== from page 25 of AT89C51RD2 Accesses to XRAM above 0FFH can only be done by the use of DPTR. ===== Notice the word "ONLY" in quotation above. Regards, Oleg