•
Register Indirect with Pre-Decrement—@–Rn
The @–Rn mode is used with MOV instructions that store register contents to memory.
It is similar to the register indirect mode, but the 16-bit general register specified in the register
field of the instruction is decremented before the operand is accessed. The size of the
decrement 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.
(5) Absolute Address—@aa:8 or @aa:16: The instruction specifies the absolute address of the
operand in memory. The MOV.B instruction uses an 8-bit absolute address of the form H'FFxx.
The upper 8 bits are assumed to be 1, so the possible address range is H'FF00 to H'FFFF (65280 to
65535). The MOV.B, MOV.W, JMP, and JSR instructions can use 16-bit absolute addresses.
(6) Immediate—#xx:8 or #xx:16: The instruction contains an 8-bit operand in its second byte, or
a 16-bit operand 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 (#xx:3) in the second or fourth byte of the
instruction, specifying a bit number.
(7) Program-Counter-Relative—@(d:8, PC): This mode is used to generate branch addresses
in the Bcc and BSR instructions. An 8-bit value in byte 2 of the instruction code is added as a
sign-extended value to the program counter contents. The result must be an even number. The
possible branching range is –126 to +128 bytes (–63 to +64 words) from the current address.
(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 from H'0000 to H'00FF (0
to 255). The word located at this address contains the branch address. The upper 8 bits of the
absolute address are 0 (H'00), thus the branch address is limited to values from 0 to 255 (H'0000 to
H'00FF). Note that some of the addresses in this range are also used in the vector table. Refer to
section 3.4, Address Space Map in Each Operating Mode.
If an odd address is specified as a branch destination or as the operand address of a MOV.W
instruction, the least significant bit is regarded as 0, causing word access to be performed at the
address preceding the specified address. See section 2.3.2, Memory Data Formats, for further
information.
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