54279



     60   DATA 205,208,240,198,204,160,0,1
        45,203,96
     70   A = USR(ADR(PGM$),START,BYTE)

     You can use this routine to clear out memory anywhere in the
     Atari. You can also use it to load any one value into memory by
     changing the second zero (after the 169) in line 40 to the value
     desired.

     Locating your graphics tables at the high end of memory may
     cause addressing problems for playfield graphics, or may leave
     some of the display unusable and cause PLOT to malfunction. If
     you locate your tables just before the screen display, it may be
     erased if you change graphics modes. You can look at your
     highest RAM use graphics statement and plan accordingly. To
     calculate a safe starting address below the display list, try:

     100 DLIST = PEEK(560) + PEEK(561) * 256: PMBASE =
      INT (DLIST/SIZE -1) * SIZE

     where SIZE is 2048 for single line resolution, 1024 for double
     line.

     Once you have the starting address, determine the ending
     address of your table by adding the correct number of bytes for
     the size (same as the SIZE variable above), and POKE this
     number (LSB/MSB) into APPMHI at locations 14 and 15 ($E, $F).
     This sets the lower limit for playfield graphics memory use. If you
     change graphics modes in the program now, it should leave your
     player tables intact. For example, if the DL is at 39968, the
     PMBASE will equal 36864 in the equation above. Add 2048
     (single line resolution) to get 38912. This is $9800. In decimal,
     the LSB is zero and the MSB is 152. POKE these values into
     APPMHI. This sets the lowest limit to which the screen and DL
     data may descend.

     The unused portion of the RAM set aside for P/M use, or any
     RAM reserved for players, but not used, may be used for other
     purposes in your program such as machine language routines.
     See the appendix for a map of P/M memory use. The register
     stores the address as below:

     Bit                  7  6  5  4  3  2  1  0
     One line resolution: ......MSB.......  ...unused...
     Two line resolution: ........MSB.........  unused..

     There are some restrictions on locating your P/M data above the
     display list. If not positioned far enough above your screen data,
     you may end up with both the normal and screen data being
     displayed at once, resulting in garbage on the screen. A display
     list may not cross a 1K boundary without a jump instruction, and