2.4
Addressing Modes
2.4.1
Addressing Mode
The H8/300 CPU supports eight addressing modes. Each instruction uses a subset of these
addressing modes.
Table 2.1 Addressing Modes
No.
(1)
(2)
(3)
(4)
Addressing Mode
Symbol
Register direct
Rn
Register indirect
@Rn
Register indirect with displacement
Register indirect with post-increment
Register indirect with pre-decrement
Absolute address
@(d:16, Rn)
@Rn+
@–Rn
(5)
(6)
(7)
(8)
@aa:8 or @aa:16
#xx:8 or #xx:16
@(d:8, PC)
@@aa:8
Immediate
Program-counter-relative
Memory indirect
(1) Register Direct—Rn: The register field of the instruction specifies an 8- or 16-bit general
register containing the operand. In most cases the general register is accessed as an 8-bit register.
Only the MOV.W, ADD.W, SUB.W, CMP.W, ADDS, SUBS, MULXU (8 bits × 8 bits), and
DIVXU (16 bits ÷ 8 bits) instructions have 16-bit operands.
(2) Register Indirect—@Rn: The register field of the instruction specifies a 16-bit general
register containing the address of the operand.
(3) Register Indirect with Displacement—@(d:16, Rn): This mode, which is used only in
MOV instructions, is similar to register indirect but the instruction has a second word (bytes 3 and
4) which is added to the contents of the specified general register to obtain the operand address.
For the MOV.W instruction, the resulting address must be even.
(4) Register Indirect with Post-Increment or Pre-Decrement—@Rn+ or @–Rn:
•
Register indirect with Post-Increment—@Rn+
The @Rn+ mode is used with MOV instructions that load registers from memory.
It is similar to the register indirect mode, but the 16-bit general register specified in the register
field of the instruction is incremented after the operand is accessed. The size of the increment
is 1 or 2 depending on the size of the operand: 1 for MOV.B; 2 for MOV.W. For MOV.W, the
original contents of the 16-bit general register must be even.
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