SMW Memory Map
|$7E0041||3 bytes||Hardware mirror||Window mask settings. These control which window is for which layer active as well as whether a window is inverted for that layer.
Format of each register:
A/a: Enable window 2
B/b: Invert window 2
C/c: Enable window 1
D/d: Invert window 1
Lower case apply for BG1, BG3 and OBJ (layer 1, 3 and sprites) and upper case apply for BG2, BG4 and COL (layer 2, 4 and colour 0 / fixed colour).
$41 (mirror of W12SEL $2123) controls BG1 and BG2
$42 (mirror of W34SEL $2124) controls BG3 and BG4
$43 (mirror of WOBJSEL $2125) controls OBJ and COL