Official Name: CheckSplitFlag
BCALL Address: 49F0
Checks if either horizontal or G-T split screen modes are active.
Z = 1 if no split screen mode is active = 0 if a split screen mode is active
grfSplitOverride, (IY + sGrFlags) = 1 to ignore split mode settings This flag is set to make system routines draw to the full screen even when in a split screen mode.