dcba&nbsp; s: sprites enable&nbsp; d: BG4 enable&nbsp; c: BG3 enable
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; b: BG2 enable&nbsp; a: BG1 enable</PRE>
The main screen designation is a way to toggle the BGs through software.&nbsp;
I think the Sub Screen designation has something to do with color add/subtract.

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<CENTER><A NAME="RegWindows"></A><FONT SIZE=+2>Windowing Registe