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.