GROUP (Treat Multiple Segments as a Single Unit)

The GROUP directive associates a group Name with one or more segments, and causes all labels and variables defined in the given segments to have addresses relative to the beginning of the group, rather than to the segments where they are defined.

Syntax

Name GROUP Segment-Name [,...]

Remarks

Each Segment-Name entry must be a unique segment name assigned by the SEGMENT directive. A Segment-Name entry may be a forward reference to a subsequently declared segment name.

An additional occurrence of a given group Name in a subsequent GROUP directive does not constitute a redefinition, but instead the effect is cumulative. The group Name itself is declared the first time it appears in a GROUP directive, but the group definition is not complete until the end of the source module is reached. The final group definition is the cumulative list of all unique segments named in all occurrences of a GROUP directive for that group Name.

Segments in a group need not be contiguous. Segments that do not belong to the group can be loaded between segments that do belong to the group. The only restriction is that for USE16 segments the distance (in bytes) between the first byte in the first segment of the group and the last byte in the last segment must not exceed 65535 bytes.

Group names can be used with the ASSUME directive and as an operand prefix with the segment override operation (:).

Example

The following example shows how to use the GROUP directive to combine segments:

In Module A:

CGROUP   GROUP    XXX,YYY
XXX      SEGMENT
         ASSUME   CS:CGROUP
         .
         .
         .
XXX      ENDS
YYY      SEGMENT
         ASSUME   CS:CGROUP
         .
         .
         .
YYY      ENDS

In Module B:

CGROUP   GROUP    ZZZ
ZZZ      SEGMENT
         ASSUME   CS:CGROUP
         .
         .
         .
ZZZ      ENDS

The next example shows how to set DS with the paragraph number of the group called DGROUP.

As immediate:

MOV      AX,DGROUP
MOV      DS,AX

In assume:

ASSUME    DS:DGROUP

As an operand prefix:

MOV    BX,OFFSET DGROUP:FOO
DW     FOO
DW     DGROUP:FOO

Note:

• DW FOO returns the offset of the symbol within its segment.

• DW DGROUP:FOO returns the offset of the symbol within the group.
The next example shows how you can use the GROUP directive to create a .COM file type.

PAGE    ,132
TITLE   GRPCOM - Use GROUP to create a DOS .COM file
;Use the DOS EXE2BIN utility to convert GRPCOM.EXE to GRPCOM.COM.

CG      GROUP    CSEG,DSEG    ;ALL SEGS IN ONE GROUP
DISPLAY MACRO    TEXT
LOCAL   MSG
DSEG    SEGMENT  BYTE PUBLIC 'DATA'
MSG     DB       TEXT,13,10,"$"
DSEG    ENDS
;;Macro produces partly in DSEG,
;;partly in CSEG
        MOV      AH,9
        MOV      DX,OFFSET CG: MSG
;;Note use of group name
;;in producing offset
        INT 21H
        ENDM
DSEG    SEGMENT  BYTE PUBLIC 'DATA'
;Insert local constants and work areas here
DSEG    ENDS
CSEG    SEGMENT BYTE PUBLIC 'CODE'
  ASSUME  CS:CG,DS:CG,SS:CG,ES:CG ;SET BY LOADER
        ORG 100H ;Skip to end of the PSP
ENTPT   PROC     NEAR ;COM file entry at 0100H
     DISPLAY "USING MORE THAN ONE SEGMENT"
     DISPLAY "YET STILL OBEYING .COM RULES"
        RET      ;Near return to DOS
ENTPT   ENDP
CSEG    ENDS
        END      ENTPT

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