12,13



     with an RTS instruction, you should set BOOT? to one and 580
     ($244) to zero.

12,13          C,D            DOSINI
     Initialization address for the disk boot. Also used to store the
     cassette-boot RUN address, which is then moved to CASINI (2,
     3). When you powerup without either the disk or an autoboot
     cassette tape, DOSINI will read zero in both locations.

14,15          E,F            APPMHI
     Applications memory high limit and pointer to the end of your
     BASIC program, used by both the OS and BASIC. It contains the
     lowest address you can use to set up a screen and Display List
     (which is also the highest address usable for programs and data
     below which the display RAM may not be placed). The screen
     handler will not OPEN the "S:" device if it would extend the
     screen RAM or the Display List below this address; memory
     above this address may be used for the screen display and other
     data (PM graphics, etc.).

     If an attempted screen mode change would extend the screen
     memory below APPMHI, then the screen is set up for GRAPHICS
     mode zero; MEMTOP (locations 741, 742; $2E5, $2E6) is updated
     and an error is returned to the user. Otherwise, the memory is not
     too small for the screen editor; the mode change will take effect
     and MEMTOP will be updated. This is one of five locations used
     by the OS to keep track of the user and display memory.
     Initialized to zero by the OS at powerup. Remember, you cannot
     set up a screen display below the location specified here.

     If you use the area below the Display List for your character sets,
     PM graphics or whatever, be sure to set APPMHI above the last
     address used so that the screen or the DL data will not descend
     and destroy your own data. See RAMTOP location 106 ($6A),
     MEMTOP at 741, 742 ($2E5, $2E6), PMBASE at 54279 ($D407)
     and CHBASE at 54281 ($D409) for more information.

Locations 16 through 127 ($10-$7F) are cleared on either cold- or
warmstart.

16             10             POKMSK
     POKEY interrupts: the IRQ service uses and alters this location.
     Shadow for 53774 ($D20E). POKE with 112 ($70; also POKE this
     same value into 53774) to disable the BREAK key. If the following
     bits are set (to one), then these interrupts are enabled (bit
     decimal values are in parentheses):

     BIT   DECIMAL   FUNCTION
      7      128     The BREAK key is enabled.
      6       64     The "other key" interrupt is enabled.