Split border is a technique similar to split rasters, except that it is handled by the CRTC instead of the [[Gate Array]].
DISPTMG can be immediately temporarily forced to 0 by using R8 (DISPTMG Skew) on CRTCs 0/3/4, or by setting R6=0 on CRTC 1. It is not possible to force DISPTMG on CRTC 2.
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