General Addressing Mode Summary - Motorola MC68030 User Manual

The postindexed indirect mode with outer displacement (see Figure 2-14)
uses the contents of An as an index to the pointer list at the displacement.
Register Xn is used as an index to the structure of data structures at the
address in the pointer. The outer displacement (od) is the displacement of
the data item within the selected data structure.
POINTER LIST
bd--~
An
POINTER
SYNTAX: ([bd,An),Xn,od)
POST·INDEXED STRUCTURE
WITH OUTER DISPLACEMENT
Figure 2-14. Postindexed Indirect Addressing with Outer Displacement
2.6.2 General Addressing Mode Summary
The addressing modes described in the previous section are derived from
specific combina,tions of options in the indexing mode or a selection of two
alternate addressing modes. For example, the addressing mode called reg-
ister indirect (Rn) assembles as the address register indirect if the register is
an address register. If Rn is a data register, the assembler uses the address
register indirect with index mode using the data register as the indirect reg-
ister and suppresses the address register by setting the base suppress bit in
the effective address specification. Assigning an address register as Rn pro-
vides higher performance than using a data register as Rn. Another case is
(bd,An), which selects an addressing mode depending on the size of the
displacement. If the displacement is 16 bits or less, the address register
indirect with displacement mode (d16,An) is used. When a 32-bit displace-
ment is required, the address register indirect with index (bd,An,Xn) is used
with the index register suppressed.
MOTOROLA
MC68030 USER'S MANUAL
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