DEY                   DEY Decrement index Y by one                    DEY

  Operation:  Y - 1 -> Y                                N V - B D I Z C
                                                        / . . . . . / .

  +----------------+-----------------------+---------+---------+----------+
  | Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
  +----------------+-----------------------+---------+---------+----------+
  |  Implied       |   DEY                 |   $88   |    1    |    2     |
  +----------------+-----------------------+---------+---------+----------+