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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.
"Where does the high byte of the address come from? Internal XRAM is - to my knowledge - not attached to P2 in any derivative (it would be ridiculous to do so)" Don't some variants have an SFR to do this? yes, most do, but not the derivative discussed. Thus "Where does the high byte ..." Erik