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3.6 M68000 Family Addressing Capability
Programs can be easily transported from one member of the M68000 Family to
another. The user object code of earlier members of the family is upwardly
compatible with later members and can be executed without change.
The
address extension word(s) are encoded with information that allows the CPU32
to distinguish new additions to the basic M68000 Family architecture.
Earlier microprocessors have no knowledge of extension word formats
implemented in later processors, and, while they do detect illegal instructions,
they do not decode invalid encodings of the extension words as exceptions.
Address extension words for the early MC68000, MC68008, MC68010, and
MC68020 microprocessors are shown in Figure 3-6.
15
I
D/A
I
D/A:
14
12
REGISTER
MC6800/MC68008/MC68010
ADDRESS EXTENSION WORD
11
10
9
8
7
I
W/L
I
0
I
0
I
0
I
DISPLACEMENT INTEGER
o
=
Data Register Select
1
=
Address Register Select
W/L
0
=
Word-Sized Operation
1
=
Long-Word-Sized Operation
CPU32/MC68020
EXTENSION WORD
15
14
12
11
10
9
8
7
I
D/A
I
REGISTER
I
W/L
I
SCALE
o
I
D/A:
0
=
Data Register Select
W/L
SCALE:
1
=
Address Register Select
o
=
Word-Sized Operation
1
=
Long-Word-Sized Operation
00
=
Scale Factor 1 (Compatible with MC68000)
01
=
Scale Factor 2 (Extension to MC68000)
10
=
Scale Factor 4 (Extension to MC68000)
11
=
Scale Factor 8 (Extension to MC68000)
DISPLACEMENT INTEGER
Figure 3-6. M68000 Family Address Extension Words
o
o
MOTOROLA
3-18
DATA ORGANIZATION AND
CPU32 REFERENCE MANUAL
ADDRESSING
CAPABILITIES
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