*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 hard scroll ====
If R3 is set to 5 instead of 6 or more, then the frame is shifted to the right on the display with an offset of half a CRTC character. This is due to the effect of shortening the C-HSYNC produced by the Gate Array.
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