Effective Address Encoding Summary; Is-Ills Memory Indirection Encodings - Motorola MC68030 User Manual

2.5 EFFECTIVE ADDRESS ENCODING SUMMARY
2-22
Most of the addressing modes use one of the three formats shown in Figure
2-4. The single effective address instruction is in the format of the instruction
word. The encoding of the mode field of this word selects the addressing
mode. The register field contains the general register number or a value that
selects the addressing mode when the mode field contains "111". Table
2-2 shows the encoding of these fields. Some indexed or indirect modes use
the instruction word followed by the brief format extension word. Other
indexed or indirect modes consist of the instruction word and the full format
of extension words. The longest instruction for the MC68030 contains 10
extension words. It is a MOVE instruction with full format extension words
for both the source and destination effective addresses and with 32-bit base
displacements and 32-bit outer displacements for both addresses. However,
coprocessor instructions can have any number of extension words. Refer to
the coprocessor instruction formats in SECTION 10 COPROCESSOR INTER-
FACE DESCRIPTION.
For effective addresses that use the full format, the index suppress (IS) bit
and the indexlindirect selection (IllS) field determine the type of indexing and
indirection. Table 2-1 lists the indexing and indirection operations corre-
sponding to all combinations of IS and IllS values.
Table 2-1. IS-IllS Memory Indirection Encodings
IS Index/Indirect Operation
0 000
No Memory Indirection
0 001
Indirect Preindexed with Null Outer Displacement
0 010
Indirect Preindexed with Word Outer Displacement
0 011
Indirect Preindexed with Long Outer Displacement
0 100
Reserved
0 101
Indirect Postindexed with Null Outer Displacement
0 110
Indirect Postindexed with Word Outer Displacement
0 111
Indirect Postindexed with Long Outer Displacement
1 000
No Memory Indirection
1
001
Memory Indirect with Null Outer Displacement
1 010
Memory Indirect with Word Outer Displacement
1
011
Memory Indirect with Long Outer Displacement
1 100-111
Reserved
MC68030 USER'S MANUAL
MOTOROLA