DEC                   DEC Decrement memory by one                     DEC

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

  +----------------+-----------------------+---------+---------+----------+
  | Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
  +----------------+-----------------------+---------+---------+----------+
  |  ZeroPage      |   DEC $FF             |   $C6   |    2    |    5     |
  |  ZeroPage,X    |   DEC $FF,X           |   $D6   |    2    |    6     |
  |  Absolute      |   DEC $FFFF           |   $CE   |    3    |    6     |
  |  Absolute,X    |   DEC $FFFF,X         |   $DE   |    3    |    7     |
  +----------------+-----------------------+---------+---------+----------+
  For penalty cycles on the 65816, check the desired addressing mode.

 65816 Extensions:

  +----------------+-----------------------+---------+---------+----------+
  | Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
  +----------------+-----------------------+---------+---------+----------+
  | Implied        |   DEC                 |   $3A   |    1    |    2     |
  +----------------+-----------------------+---------+---------+----------+