54274,5



     seven) are read, as below:

     Decimal        0     1     2     3     4     5     6     7
     Cursor
     Transparent    X           X           X           X
     Opaque               X           X           X           X
     Present                    X     X                 X     X
     Absent         X     X                 X     X
     ----------------------------------------------------------------------
     Characters
     Normal         X     X     X     X
     Inverted                               X     X     X     X

54274,5        D402,3         DLISTL/H
     Display list pointer. Tells the OS the address of the display list
     instructions about what screen mode(s) to display and where to
     find the screen data. See SDLIST (560, 561; $230, $231).

54276          D404           HSCROL
     (W) Horizontal scroll enable, POKE HSCROL with from zero to
     16 clock cycles for the number of cycles to scroll. Horizontal fine
     scrolls can be used only if BIT 4 of the display list instruction is
     set. The difficulty in horizontal scrolling lies in arranging the
     screen data to be scrolled in such a manner as to prevent
     wraparound (i.e., the bit or byte scrolled off screen in one line
     becomes the bit or byte scrolled on screen in an adjacent line).
     Normal data arranged for TV display looks like this on the screen:

          +----------+
          |..........|
          |..........|
          |..........|
          |..........|
          |..........|
          |..........|
          +----------+

     where it is a one-dimensional memory area "folded" at the proper
     places to create the image of a two dimensional screen. This is
     done by the DL character or map mode instruction. Without
     other instructions, it reads the memory continuously from the first
     specified location, each line taking the correct number of bytes
     for the GRAPHICS mode specified. To properly scroll it
     horizontally, you must arrange it in relation to the TV screen like
     this:

          +----------+
     .....|..........|.....
     .....|..........|.....
     .....|..........|.....
     .....|..........|.....
     .....|..........|.....
     .....|..........|.....
          +----------+