Datasheet

Addressing Modes
MC68HC812A4 Data Sheet, Rev. 7
Freescale Semiconductor 47
3.5 Addressing Modes
Addressing modes determine how the CPU accesses memory locations to be operated upon. The CPU12
includes all of the addressing modes of the M68HC11 CPU as well as several new forms of indexed
addressing. Table 3-1 is a summary of the available addressing modes.
Table 3-1. Addressing Mode Summary
Addressing Mode Source Format Abbreviation Description
Inherent INST INH Operands (if any) are in CPU registers.
Immediate
INST #opr8i
or
INST #opr16i
IMM
Operand is included in instruction stream.
8- or 16-bit size implied by context
Direct INST opr8a DIR
Operand is the lower 8 bits of an address in the range
$0000–$00FF.
Extended INST opr16a EXT Operand is a 16-bit address
Relative
INST rel8
or
INST rel16
REL
An 8-bit or 16-bit relative offset from the current pc is
supplied in the instruction.
Indexed
(5-bit offset)
INST oprx5,xysp IDX 5-bit signed constant offset from x, y, sp, or pc
Indexed
(auto pre-decrement)
INST oprx3,–xys IDX Auto pre-decrement x, y, or sp by 1 ~ 8
Indexed
(auto pre-increment)
INST oprx3,+xys IDX Auto pre-increment x, y, or sp by 1 ~ 8
Indexed
(auto
post-decrement)
INST oprx3,xys– IDX Auto post-decrement x, y, or sp by 1 ~ 8
Indexed
(auto post-increment)
INST oprx3,xys+ IDX Auto post-increment x, y, or sp by 1 ~ 8
Indexed
(accumulator offset)
INST abd,xysp IDX
Indexed with 8-bit (A or B) or 16-bit (D) accumulator
offset from x, y, sp, or pc
Indexed
(9-bit offset)
INST oprx9,xysp IDX1
9-bit signed constant offset from x, y, sp, or pc
(lower 8-bits of offset in one extension byte)
Indexed
(16-bit offset)
INST oprx16,
xysp IDX2
16-bit constant offset from x, y, sp, or pc
(16-bit offset in two extension bytes)
Indexed-indirect
(16-bit offset)
INST [oprx16,xysp][IDX2]
Pointer to operand is found at...
16-bit constant offset from x, y, sp, or pc
(16-bit offset in two extension bytes)
Indexed-indirect
(D accumulator
offset)
INST [D,xysp][D,IDX]
Pointer to operand is found at...
x, y, sp, or pc plus the value in D