DPPx: operand

The data page pointers (DPP0-DPP3) may be used to override the default page assumptions defined using the ASSUME control statement.

Each variable in your program is located somewhere in memory. The 16K page containing a particular variable is the parent page for that variable and is specified by a Data Page Pointer (DPP). Normally, the assembler tracks DPPs by means of the ASSUME control and implicitly uses the appropriate DPP when to access a variable.

Page override operators (DPP0-DPP3) override the ASSUME control and directly specify the DPP to use. To get a valid run-time address, you must ensure that the DPP is loaded with the correct base page number.

ASSUME DPP2:D100

D100   SECTION DATA
       V1   DSW  1
       V2   DSW  1
D100   ENDS

C100   SECTION CODE
       MOV    DPP2,#D100        ; establish data-page addressability
       NOP               ; pipeline delay
       MOV    R10,V1    ; DPP2:V1 used per ASSUME

       MOV    DPP1,#D100        ; set up DPP1 for later override
       NOP
       MOV    R13,DPP1:V2       ; addressing per DPP1; overriding ASSUME
C100   ENDS