Addressing Modes — IX1
Instructions that use indexed addressing with 8-bit offsets can read from or write to any memory location between $0000 and $01FE inclusive.
All read-modify-write instructions support this addressing mode…
ASL $00,X ASR $FF,X CLR $02,X COM $FD,X DEC $04,X INC $FB,X LSL $06,X LSR $F9,X NEG $08,X ROL $F7,X ROR $0A,X TST $F5,X
Likewise, all instructions that can use direct addressing can also use indexed addressing with 8-bit offsets.
Notes:
Instructions that use indexed addressing with an 8-bit offset have access to the first 511 locations in memory. These instructions execute in one less cycle and require one less byte of storage than their counterparts that use 16-bit offsets.
Target addresses are formed by taking the unsigned sum of the 8-bit offset and the contents of the index register and can range from $0000 (offset = $00 and X = $00) to $01FE (offset = $FF and X = $FF).
Most 68HC05 devices have 512 bytes of RAM or less, which makes indexed addressing with 8-bit offsets especially useful for operations on tabular or string data maintained in on-chip RAM.