C166/ST10 Cross-Assembler, Linker/Locator, Utilities ... - Tasking

4−14
LANGUAGE
4.5.5 PAGE EXTEND AND SEGMENT EXTEND
INSTRUCTIONS
Chapter 4
The instructions EXTP, EXTPR and EXTSR cause the assembler to change
checks on the operands in the extend block. The page extend instructions
cause the processor to use the page number supplied with the page
extend instruction instead of the page number in a DPP register. The
segment extend instructions cause the processor to use the segment
number supplied with the segment extend instruction instead of
addressing via the page number in a DPP register.
Because the DPP registers are not used for addressing in a page extend or
segment extend block, a DPP number in bit 14 and 15 of an operand is
not allowed. So, each operand (label or expression) which expects a DPP
prefix outside a page extend or segment extend block, should not have a
DPP prefix or a DPP assumption (ASSUME directive) inside a page extend
block. If a DPP prefix or DPP assumption is used in a page extend or
segment extend block, the assembler issues a warning. This warning is not
issued if the POF operator is used for such an operand in a page extend
block or if the POF or SOF operator is used for such an operand in a
segment extend block. The POF or SOF operator should be the first
operator of an expression.
Example:
EXTP #PAG labx, #1 ; extend page
MOV R0, labx ; labx is NOT assumed: ok
EXTERN DPP0:labe:WORD
EXTP #PAG labe, #2 ; extend page
MOV R0, labe ; labe has DPP prefix:
; warning!
MOV R0, POF labe ; POF overrides DPP: ok
The extend page and extend segment instructions can only be used in the
SEGMENTED and NONSEGMENTED/SMALL memory model.