The TIA (as seen by the programmer)

9.0 Object Priorities

Each object is assigned a priority so when any two objects overlap the one with the highest priority will appear to move in front of the other. To simplify hardware logic, the missiles have the same priority as their associated player, and the ball has the same priority as the playfield. The background, of course, has the lowest priority. The following table illustrates the normal (default) priority assignments.

               Priority       Objects
               1              P0, M0
               2              P1, M1
               3              BL, PF
               4              BK

This priority assignment means that players and missiles will move in front of the playfield. To make the players and missiles move behind the playfield, a "1" must be written to D2 of the CTRLPF register. The following table illustrates how the priorities are affected:

               Priority       Objects
               1              PF, BL
               2              P0, M0
               3              P1, M1
               4              BK

One more priority control is available to be used for displaying the score. When a "1" is written to D1 of the CTRLPF register, the left half of the playfield takes on the color of player 0, and the right half the color of player 1. The game score can now be displayed using the PF graphics register, and the score will be in the same color as its associated player.

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See also: 'TIA 1A - TELEVISION INTERFACE ADAPTOR (MODEL 1A) - 8.5 Priority Encoder'