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

7−10
DIRECTIVES
Chapter 7
This keyword enables the addressability of system ranges (via
SFR) in SEGMENTED mode, if a SFR is used in a virtual
operand combination.
The SYSTEM keyword can also be used in a DGROUP
directive, which causes a whole group to be located in the
system page (page 3). If this group is assumed to a DPP,
SYSTEM is also assumed. If SYSTEM is assumed, it implies
that the whole group is assumed also.
Example:
The following example illustrates the use of ASSUME.
$SEGMENTED
DSEC1 SECTION DATA
AWORD DW 0
DSEC1 ENDS
DSEC2 SECTION DATA
BYTE1 DB 0
DSEC2 ENDS
DSEC3 SECTION DATA
BYTE2 DB 0
DSEC3 ENDS
CSEC SECTION CODE
ASSUME DPP0:DSEC1, DPP1:DSEC3
MOV DPP0, #DSEC1
MOV DPP1, #DSEC3
MOV DPP2, #DSEC2
.
.
MOV R0, AWORD ; The ASSUME covers the reference.
. ; DPP0 points to the base of
. ; section DSEC1 that contains AWORD
.
MOV RL1, DPP2:BYTE1 ; Explicit code. The page override
. ; operator covers the reference
MOV RL1, BYTE1 ; Error!: No DPP register used and
. ; no ASSUME has been made.
.
MOV RL2, BYTE2 ; The ASSUME covers the reference.
. ; DPP1 points to the base of
. ; section DSEC3 that contains BYTE2
CSEC ENDS