4.18 Memory accesses

Many load and store instructions support different addressing modes.

Offset addressing

The offset value is applied to an address obtained from the base register. The result is used as the address for the memory access. The base register is unchanged. The assembly language syntax for this mode is:

[Rn, offset]
Pre-indexed addressing

The offset value is applied to an address obtained from the base register. The result is used as the address for the memory access, and written back into the base register. The assembly language syntax for this mode is:

[Rn, offset]!
Post-indexed addressing

The address obtained from the base register is used, unchanged, as the address for the memory access. The offset value is applied to the address, and written back into the base register. The assembly language syntax for this mode is:

[Rn], offset

In each case, Rn is the base register and offset can be:

  • An immediate constant.
  • An index register, Rm.
  • A shifted index register, such as Rm, LSL #shift.
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