Datasheet

Central Processing Unit
Technical Data MC68HC912DT128A — Rev 4.0
38 Central Processing Unit MOTOROLA
2.5 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 2-1 is a summary of the available addressing modes.
Table 2-1. M68HC12 Addressing Mode Summary
Addressing Mode Source Format Abbreviation Description
Inherent
INST
(no externally supplied
operands)
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
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cale Semiconductor,
I
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