Indexed-indirect addressing

In this rarely used Addressing mode, X index register is used to offset the zero page vector used to determine the effective address. Put another way, the vector is chosen by adding the value in the X index register to the given zero page address. The resulting zero page address is the vector from which the effective address is read.

Indexed-indirect addressing is written as follows:

     LDX #$00
     LDA ($02,X)

In the above case, X is loaded with zero (0), so the vector is calculated as $02 plus zero (0). The resulting vector is ($02). If zero page memory $02 contains 00 80, then the effective address from the vector (02) would be $8000.

This addressing mode would only be useful to select a vector from an array of zero page vectors, and as such is very rarely used.