
MOTOROLA
Chapter 2. Programming Model
2-19
Environments Manual
for more information about big-endian and little-endian byte
ordering.
The operand of a single-register memory access instruction has a natural alignment
boundary equal to the operand length. In other words, the “natural” address of an operand
is an integral multiple of the operand length. A memory operand is said to be aligned if it
is aligned at its natural boundary; otherwise it is misaligned. For a detailed discussion about
memory operands, see Chapter 3, “Operand Conventions,” in
The Programming
Environments Manual
.
2.3.2.3 Effective Address Calculation
An effective address (EA) is the 32-bit sum computed by the processor when executing a
memory access or branch instruction or when fetching the next sequential instruction. For
a memory access instruction, if the sum of the effective address and the operand length
exceeds the maximum effective address, the memory operand is considered to wrap around
from the maximum effective address through effective address 0, as described in the
following paragraphs.
Effective address computations for both data and instruction accesses use 32-bit unsigned
binary arithmetic. A carry from bit 0 is ignored.
Load and store operations have three categories of effective address generation:
Register indirect with immediate index mode
Register indirect with index mode
Register indirect mode
Refer to Section 2.3.4.3.2, “Integer Load and Store Address Generation,” for further
discussion of effective address generation for load and store operations.
Branch instructions have three categories of effective address generation:
Immediate
Link register indirect
Count register indirect
Refer to Section 2.3.4.4.1, “Branch Instruction Address Calculation,” for further discussion
of branch instruction effective address generation.
2.3.2.4 Synchronization
The sychronization described in this section refers to the state of the processor that is
performing the sychronization.