*Bits 7..4 define Vertical Sync Width. If 0 is programmed this gives 16 lines of VSYNC.
*Bits 3..0 define Horizontal Sync Width. If 0 is programmed this gives a HSYNC width of 16.
==== R3 fine horizontal hardware scroll ====
If R3l is set to 5 instead of 6 or more, then the frame is shifted to the right on the CTM monitor with an offset of half a CRTC character. This is due to the effect of shortening the C-HSYNC produced by the [[Gate Array]].
Even further, continuously switching these values between each raster line, instead of once per frame, will divide by 2 the difference between the 2 positions and so will give an offset of a quarter of a CRTC character.
And smartly combining R2 and R3 horizontal screen wobbling effects at every raster line will give 1-pixel mode1 horizontal hardware scroll.
As these effects rely on invalid video signals, they are badly supported on modern displays.
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