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The EDATA memory is only available in the NXP 80C51MX.

In the NXP 80C51MX, the EDATA memory can be accessed via EPTR or the Universal Pointers PR0 and PR1. Universal Pointers can access any memory location in the 16MB address space.

Example for NXP 80C51MX
?ED?my_seg SEGMENT EDATA                ; define a SEGMENT of class EDATA
           RSEG    ?ED?my_seg
STRING:    DS      100                  ; reserve 100 Bytes

?PR?myprog SEGMENT CODE                 ; define a segment for program code
           RSEG    ?PR?myprog
           MOV      R1,#BYTE0 STRING    ; load address of STRING in PR0
           MOV      R2,#BYTE1 STRING
           MOV      R3,#BYTE2 STRING
           MOV      A,@PR0              ; load first byte of STRING in A
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