APPENDIX TWELVE



     Entry        Handler or Use
     51658/C9CA   Invoke parallel device handler
     51753/CA29   Load and initialize peripheral handler
     51799/CA57   Start of self-test offsets and text (uses hard-
                  ware values for character display)
     52054/CB56   Checksum linkage table

52224-53247    CC00-CFFF      CHARSET2
     International character set, assembled in the same manner as
     the standard character set at 57344 ($E000). There are two
     character sets in the XL series, and you can switch between
     them by POKE 756,224 (standard) or POKE 756,204
     (international).

53279          D01F           CONSOL
     If you hold down the OPTION key when booting an application
     on the XL, you disable BASIC (but no other cartridge), allowing
     the memory space to be used for applications, You generally
     need to keep the key held down only for the first few seconds of
     the boot.

53504-53759    D100-D1FF      ....
     Unused in both the 400/800 and XL models by the OS, this area
     is switched out when an external device connected to the
     expansion bus is selected and the device memory switched in.
     The situation is reversed when the device I/O is completed.

     Locations     Hex         Use
     53504-53758   D100-D1FE   Device registers
     53504         D100        Hardware get and put register
                               (HWGET, HWPUT); data from
                               the device on the bus is stored
                               here.
     53505         D101        Hardware reset and status reg-
                               ister (HWRSET for write--this re-
                               sets the get/put register;
                               HWSTAT for read).
     53759         D1FF        Hardware select register, shad-
                               owed by byte 583 ($247). Bit 0
                               is device 0, bit 1 device 1, and
                               so on. Writing to this byte de-
                               selects the FP ROM and selects
                               the device ROM (try looking at
                               it and subsequent locations
                               with MAC/65's DDT or a similar
                               tool while altering $D1FF).