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(4) Register Indirect with Post-Increment or Pre-Decrement—@ERn+ or @-ERn:
• Register indirect with post-increment—@ERn+
The register field of the instruction code specifies an address register (ERn) which contains the
address of a memory operand. After the operand is accessed, 1, 2, or 4 is added to the address
register contents and the sum is stored in the address register. The value added is 1 for byte
access, 2 for word transfer instruction, or 4 for longword transfer instruction. For word or
longword transfer instruction, the register value should be even.
• Register indirect with pre-decrement—@-ERn
The value 1, 2, or 4 is subtracted from an address register (ERn) specified by the register field
in the instruction code, and the result becomes the address of a memory operand. The result is
also stored in the address register. The value subtracted is 1 for byte access, 2 for word transfer
instruction, or 4 for longword transfer instruction. For word or longword transfer instruction,
the register value should be even.
(5) Absolute Address—@aa:8, @aa:16, @aa:24, or @aa:32: The instruction code contains the
absolute address of a memory operand. The absolute address may be 8 bits long (@aa:8), 16 bits
long (@aa:16), 24 bits long (@aa:24), or 32 bits long (@aa:32).
To access data, the absolute address should be 8 bits (@aa:8), 16 bits (@aa:16), or 32 bits
(@aa:32) long. For an 8-bit absolute address, the upper 24 bits are all assumed to be 1 (H'FFFF).
For a 16-bit absolute address the upper 16 bits are a sign extension. A 32-bit absolute address can
access the entire address space.
A 24-bit absolute address (@aa:24) indicates the address of a program instruction. The upper 8
bits are all assumed to be 0 (H'00).
Table 2-5 indicates the accessible absolute address ranges.
Table 2-5
Absolute Address Access Ranges
Absolute Address
Data address
Program instruction
address
Note: * Not available in the H8S/2646 Series.
Normal Mode*
8 bits (@aa:8)
H'FF00 to H'FFFF
16 bits (@aa:16)
H'0000 to H'FFFF
32 bits (@aa:32)
24 bits (@aa:24)
Advanced Mode
H'FFFF00 to H'FFFFFF
H'000000 to H'007FFF,
H'FF8000 to H'FFFFFF
H'000000 to H'FFFFFF
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