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15
14
13
12
X
X
X
15
14
12
D/A
REGISTER
15
14
12
D/A
REGISTER
Field
Instruction
Register
Extension
Register
D/A
W/L
Scale
*Memory indirect addressing will cause illegal instruction trap; must be = 000 if IS = 1
Figure 3-2 Effective Address Specification Formats
EA modes can be classified as follows:
Data
Memory
Alterable
Control
Categories are sometimes combined, forming new, more restrictive, categories. Two
examples are alterable memory or alterable data. The former refers to addressing
modes that are both alterable and memory addresses; the latter refers to addressing
modes that are both alterable and data addresses. Table 3-1 shows categories to
which each of the EA modes belong.
MOTOROLA
DATA ORGANIZATION AND ADDRESSING CAPABILITIES
3-10
SINGLE EA INSTRUCTION FORMAT
11
10
9
X
X
X
X
BRIEF FORMAT EXTENSION WORD
11
10
9
W/ L
SCALE
FULL FORMAT EXTENSION WORD(S)
11
10
9
W/ L
SCALE
BASE DISPLACEMENT (0, 1, OR 2 WORDS)
Definition
General Register Number
Index Register Number
Index Register Type
0 = Dn
1 = An
Word/Long Word Index Size
0 = Sign-Extended Word
1 = Long Word
Scale Factor
00 = 1
01 = 2
10 = 4
11 = 8
A data addressing EA mode refers to data operands.
A memory addressing EA mode refers to memory operands.
An alterable addressing EA mode refers to writable operands.
A control addressing EA mode refers to unsized memory operands.
8
7
6
5
X
X
X
8
7
0
DISPLACEMENT
8
7
6
5
1
BS
IS
BD SIZE
Field
Definition
BS
Base Register Suppress
0 = Base Register Added
1 = Base Register Suppressed
IS
Index Suppress
0 = Evaluate and Add Index Operand
1 = Suppress Index Operand
BD SIZE
Base Displacement Size
00 = Reserved
01 = Null Displacement
10 = Word Displacement
11 = Long-Word Displacement
I/IS *
Index/Indirect Selection
Indirect and Indexing Operand
Determined in Conjunction with Bit 6,
Index Suppress
4
3
2
1
EFFECTIVE ADDRESS
MODE
REGISTER
4
3
2
0
I/IS
REFERENCE MANUAL
0
0
0
CPU32
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