The HSYNC width value is interpreted differently between CRTCs. On CRTCs 0/1, if 0 is programmed no HSYNC is generated. On CRTCs 2/3/4, if 0 is programmed this gives a HSYNC width of 16.
CRTCs 1/2 have a fixed VSYNC width value of 16. VSYNC width can be configured with Register 3 R3 on CRTCs 0/3/4. If 0 is programmed this gives 16 lines of VSYNC.
On CRTCs 0/3/4, even if the number of lines of VSYNC is set to 1 in R3, the Gate Array will perform a full VSYNC of 26 lines (including 4 lines of C-VSYNC to the monitor). This is also true if the duration of the CRTC VSYNC is reduced to 2 µseconds.