Undocumented or Lesser known Register Settings

[peteym5]

How many use some of these undocumented or lesser known register settings for the Antic, GTIA, Pokey, chips. To create a graphics mode, effect, or sound.

I know something called "PRIORITY ZERO" that "OR" effect certain player/missiles to the playfield colors. Player 0 & 1 OR with Playfield 0 & 1,  Player 2 & 3 OR with Playfield 2 & 3. I usually set PRIOR to 1 to put the players on top of the play field. What was funny, a few times I forgot to set the PRIOR register and noticed something weird going on, but never thought about actually using the settings. I think there is a Tetris clone out there that takes advantage of it. 

 

Edited September 24, 2019 by peteym5

[RickR]

I know there are several revisions of Antic and GTIA.  I wonder if any of these tricks were "corrected" in later revisions?

 

[peteym5]

Actually this Player/Missile priority thing worked on all Atari's since the 400/800 and did the same thing with XL/XE. I know some GTIA chips lacked the 16 color modes because of a manufacturing issue, so Atari just designated two chips as CTIA and GTIA.