APPENDIX TWELVE



     Vector      Hex         Label      Points to
     532,533     214,215     VTIMR3     49357 ($C0CD)
     534,535     216,217     VIMIRQ     49200 ($C030)
     546,547     222,223     VVBLKI     49378 ($C0E2)
     548,549     224,225     VVBLKD     49802 ($C28A)
     550,551     226,227     CDTMA1     60433 ($EC11)

     The OS was rewritten in the XL/XE models, moving the interrupt
     handlers down into the previously unused region 49152-53247
     ($C000-$CFFF).

563            233            LCOUNT
     Temporary counter for peripheral handler loader.

566,567        236,237        BRKKY
     Now points to 49298 ($C092).

568,569        238,239        RELADR(1200XL)
                              VPIRQ (All XL/XEs
                              except 1200XL)
     Previously spare bytes, now the address of the relocatable
     loader routine in the 1200XL and vector for parallel bus inter-
     rupt requests on all XL/XEs except 1200XL (where it points to a
     routine at 51566; $C96E)--the vector for any initialized generic
     parallel device.

581            245            RECLEN
     Relocatable loader routine variable for record length.

583-618        $247-$26A      ....
     Reserved (unused) on the 1200XL.

583            247            PDVMSK
     Shadow mask for the device selection register at 53759 ($D1FF;
     active only when the OS deselects the floating-point ROM by
     writing to that address). You can run up to eight parallel de-
     vices through the bus; each bit in this register corresponds to
     one device. The mask must be set for the proper device before
     the OS will allow an IRQ to be sent to that device.

584            248            SHPDVS
     Shadow for parallel bus register; each bit represents one of
     eight parallel devices. Allows the OS to service VBIs while run-
     ning the device masked by this bit.

585            249            PDMSK
     Parallel bus interrupt mask; allows OS to service IRQs from the
     device masked by the bit in this register. See above.