ISB                    ISB INC memory, SBC memory                     ISB
                                                     N V - B D I Z C
  Operation:  M <- (M) + 1, A <- (A) - M - C         ? ? - - - - ? ?

  +----------------+-----------------------+---------+---------+----------+
  | Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
  +----------------+-----------------------+---------+---------+----------+
  |  Zeropage      |   ISB $FF             |   $E7   |    2    |    5     |
  |  Zeropage,X    |   ISB $FF,X           |   $F7   |    2    |    6     |
  |  Absolute      |   ISB $FFFF           |   $EF   |    3    |    6     |
  |  Absolute,X    |   ISB $FFFF,X         |   $FF   |    3    |    7*    |
  |  Absolute,Y    |   ISB $FFFF,Y         |   $FB   |    3    |    7*    |
  |  (Indirect,X)  |   ISB ($FF,X)         |   $E3   |    3    |    8     |
  |  (Indirect),Y  |   ISB ($FF),Y         |   $F3   |    2    |    8*    |
  +----------------+-----------------------+---------+---------+----------+
  * Add 1 if page boundary is crossed.