53248



     the former method will you be able to get a readable screen,
     however. In the latter you will only create a four line, scrolling,
     unreadable window. You will be able to input and output as with
     any normal text window; you just won't be able to read it! GTIA,
     by the way, apparently stands for "George's Television Interface
     Adapter." Whoever George is, thanks, but what is CTIA?
     See the OS User's Manual, the Hardware Manual, De Re Atari and
     COMPUTE!, July 1982 to September 1982, for more information.

53248          D000           HPOSP0
     (W) Horizontal position of player 0. Values from zero to 227 ($E3)
     are possible but, depending on the size of the playfield, the range
     can be from 48 ($30) as the leftmost position to 208 ($D0) as the
     rightmost position. Other positions will be "off screen."
     Here are the normal screen boundaries for players and missiles.
     The values may vary somewhat due to the nature of your TV
     screen. Players and missiles may be located outside these
     boundaries, but will not be visible (off screen):

                               Top
                           32 for single,
                        16 for double line
                            resolution
                  +--------------------------------+
                  |                                |
                  |                                |
                  |                                |
     48 for both  |                                | 208 for both
     resolutions  |                                | resolutions
                  |                                |
                  |                                |
                  |                                |
                  +--------------------------------+
                              Bottom
                          224 for single,
                        112 for double line
                             resolution

     Although you can POKE to these horizontal position registers, they
     are reset to zero immediately. The player or missile will stay on the
     screen at the location specified by the POKE, but in order to move
     it using the horizontal position registers, you can't use:

     POKE 53248, PEEK (53248) + n (or -n)

     which will end up generating an error message. Instead, you need
     to use something like this:

     10   POKE 704,220: GRAPHICS 1: HPOS =
         53248: POKE 623,8