General Addressing Mode Summary - Motorola MC68030 User Manual

Data Organization and Addressing Capabilities
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.
SYNTAX: ([bd,An],Xn,od)
POSTINDEXED STRUCTURE
POINTER LIST
WITH OUTER DISPLACEMENT
bd
od
An
Xn
POINTER DATA ITEM
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
combinations of options in the indexing mode or a selection of two alternate addressing
modes. For example, the addressing mode called register 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 register and suppresses the address register by setting the base suppress bit in the
effective address specification. Assigning an address register as Rn provides 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 (d ,An) is used. When a 32-
16
bit displacement is required, the address register indirect with index (bd,An,Xn) is used with
the index register suppressed.
2-32 MC68030 USER'S MANUAL MOTOROLA