APPENDIX TWELVE



586,587        24A,24B        RELADR
     Relocatable loader relative address.

588,589        24C,24D        PPTMPA,PPTMPX
     One-byte temporary storage registers for relocatable loader.

590-618        24E-26A        ....
     Spare bytes, reserved for future use.

619            26B            CHSALT
     Alternate character set pointer for the 1200XL, initialized to 204
     ($CC) to point to the international character set as the next set
     to display on the CTRL-F4 toggle. The XL has two internal
     character sets, one at 52224 ($CC00) and the other at 57344
     ($E000).

620            26C            VSFLAG
     Fine-scroll temporary register.

621            26D            KEYDIS
     Keyboard disable. POKE with 255 to disable the keyboard, 0 to
     reenable. You have to press RESET (all XL/XEs except 1200XL) to
     get control back if you are locked out; 1200XL users can press
     CTRL-F1 (toggles it on and off; LED 1 is on when the keyboard is
     disabled).

622            26E            FINE
     Fine-scroll enable for graphics mode 0 (text); POKE with 0 for
     coarse scrolling (the default) and 255 ($FF) for fine scrolling.
     Follow the POKE with GR.0 or an OPEN for device E:. Try listing
     a long program--it's slow and smooth! The display list for fine
     scrolling is one byte longer than for coarse scrolling. The OS
     places the address (64708; $FCC4) of a Display List Interrupt
     (DLI) at 512, 513 ($200,201), replacing any you might have
     placed there. The color register at 53271 ($D017) is altered for
     the last visible screen line.

     If you enable fine scrolling and go immediately to DOS, you'll
     see that it's still enabled when you do a copy to screen or disk
     directory. Jerry White wrote an article demonstrating fine
     scrolling and other XL features in Analog, February 1984.

628-631        272-277        PADDL4-7
     The XL has only two ports, so only paddles 0-3 are active.

634-635        27A-27B        STICK2-3
     No longer in use since there are ports only for sticks 0 and 1.