TAY                TAY Transfer accumulator to index Y                TAY

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

  +----------------+-----------------------+---------+---------+----------+
  | Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
  +----------------+-----------------------+---------+---------+----------+
  |  Implied       |   TAY                 |   $A8   |    1    |    2     |
  +----------------+-----------------------+---------+---------+----------+

What it does: Transfers the byte in the Accumulator to the Y Register.

Major uses: Sometimes you can copy the byte in the Accumulator into the Y Register as a way of briefly storing the byte until it's needed again by the Accumulator. If Y is currently unused, TAY is a convenient alternative to PHA (another temporary storage method).

However, since Y is quite often employed as a loop counter, TAY is a relatively rarely used instruction.