Datasheet

Data Types
M68HC12B Family Data Sheet, Rev. 9.1
Freescale Semiconductor 63
3.4 Data Types
The CPU12 supports four data types:
1. Bit data
2. 8-bit and 16-bit signed and unsigned integers
3. 16-bit unsigned fractions
4. 16-bit addresses
A byte is eight bits wide and can be accessed at any byte location. A word is composed of two consecutive
bytes with the most significant byte at the lower value address. There are no special requirements for
alignment of instructions or operands.
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)
Table continued on next page