PHA                   PHA Push accumulator on stack                   PHA

  Operation:  A to Stack                                N V - B D I Z C
                                                        . . . . . . . .

  +----------------+-----------------------+---------+---------+----------+
  | Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
  +----------------+-----------------------+---------+---------+----------+
  |  Implied/Stack |   PHA                 |   $48   |    1    |    3     |
  +----------------+-----------------------+---------+---------+----------+
  For penalty cycles on the 65816, check the desired addressing mode.

What it does: Pushes the Accumulator onto the stack.

Major uses: To temporarily (very temporarily) save the byte in the Accumulator. If you are within a particular subroutine and you need to save a value for a brief time, you can PHA it. But beware that you must PLA it back into the Accumulator before any RTS so that it won't misdirect the computer to the wrong RTS address. All RTS addresses are saved on the stack. Probably a safer way to temporarily save a value (a number) would be to STA TEMP or put it in some other temporary variable that you've set aside to hold things. Also, the values of A, X, and Y need to be temporarily saved, and the programmer will combine TYA and TXA with several PHAs to stuff all three registers onto the stack. But, again, matching PLAs must restore the stack as soon as possible and certainly prior to any RTS.