Hi, I'm using the T89C51AC2 from Atmel. It had a Dual DPTR. ; MR = windows Main register in virtual Machine ( simulator ) org 0 AUXR1 DATA 0A2H MOV DPTR,#01H ; VALUE DPTR IN window MR 0001 INC AUXR1 ;switch to DPTR1 VALUE DPTR IN window MR 0001 MOV DPTR,#02H VALUE DPTR IN window MR 0002 INC AUXR1 ;switch to DPTR0 * VALUE DPTR IN window MR 0002 INC AUXR1 ;* VALUE DPTR IN window MR 0002 INC AUXR1 ;* VALUE DPTR IN window MR 0002 INC AUXR1 ;* VALUE DPTR IN window MR 0002 INC AUXR1 ;* VALUE DPTR IN window MR 0002 nop END