Addressing Modes — IX
The target address for an instruction that uses indexed addressing without an offset is simply the contents of the index register zero extended to 16 bits.
All read-modify-write instructions support this addressing mode…
ASL ,X ASR ,X CLR ,X COM ,X DEC ,X INC ,X LSL ,X LSR ,X NEG ,X ROL ,X ROR ,X TST ,X
All instructions that can use direct addressing and indexed addressing with 8-bit offsets can also use indexed addressing without offsets.
Notes:
Instructions that use indexed addressing without offsets can only access memory locations $00 to $FF. Target addresses for these instructions are formed by zero extending the contents of the 8-bit index register to 16 bits.
This is the fastest indexed addressing mode, with instructions needing one less cycle to execute than if an 8-bit offset if used. Looked at differently, these instructions execute as quickly as their direct mode counterparts but require only one byte of storage.