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The register field of the instruction specifies a 16-bit general register containing the address of
the operand. After the operand is accessed, the register is incremented by 1 for MOV.B or 2 for
MOV.W. For MOV.W, the original contents of the 16-bit general register must be even.
• Register indirect with pre-decrement—@–Rn
The @–Rn mode is used with MOV instructions that store register contents to memory.
The register field of the instruction specifies a 16-bit general register which is decremented by
1 or 2 to obtain the address of the operand in memory. The register retains the decremented
value. The size of the decrement is 1 for MOV.B or 2 for MOV.W. For MOV.W, the original
contents of the register must be even.
5. Absolute Address—@aa:8 or @aa:16: The instruction specifies the absolute address of the
operand in memory.
The absolute address may be 8 bits long (@aa:8) or 16 bits long (@aa:16). The MOV.B and bit
manipulation instructions can use 8-bit absolute addresses. The MOV.B, MOV.W, JMP, and
JSR instructions can use 16-bit absolute addresses.
For an 8-bit absolute address, the upper 8 bits are assumed to be 1 (H'FF). The address range is
H'FF00 to H'FFFF (65280 to 65535).
6. Immediate—#xx:8 or #xx:16: The instruction contains an 8-bit operand (#xx:8) in its second
byte, or a 16-bit operand (#xx:16) in its third and fourth bytes. Only MOV.W instructions can
contain 16-bit immediate values.
The ADDS and SUBS instructions implicitly contain the value 1 or 2 as immediate data. Some
bit manipulation instructions contain 3-bit immediate data in the second or fourth byte of the
instruction, specifying a bit number.
7. Program-Counter Relative—@(d:8, PC): This mode is used in the Bcc and BSR
instructions. An 8-bit displacement in byte 2 of the instruction code is sign-extended to 16 bits
and added to the program counter contents to generate a branch destination address. The
possible branching range is –126 to +128 bytes (–63 to +64 words) from the current address.
The displacement should be an even number.
8. Memory Indirect—@@aa:8: This mode can be used by the JMP and JSR instructions. The
second byte of the instruction code specifies an 8-bit absolute address. The word located at this
address contains the branch destination address.
The upper 8 bits of the absolute address are assumed to be 0 (H'00), so the address range is
from H'0000 to H'00FF (0 to 255). Note that with the H8/300L Series, the lower end of the
address area is also used as a vector area. See 3.3, Interrupts, for details on the vector area.
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