XFree86 Video Timings HOWTO : Black Magic and Sync Pulses
Previous: Computing Frame Sizes Next: Putting it All Together
9. Black Magic and Sync Pulses  OK, now you've computed HFL/VFL
numbers for your chosen dot clock, found the refresh rate
acceptable, and checked that you have enough VRAM. Now for the
real black magic -- you need to know when and where to place
synchronization pulses.  The sync pulses actually control the
horizontal and vertical scan frequencies of the monitor. The HSF
and VSF you've pulled off the spec sheet are nominal,
approximate maximum sync frequencies. The sync pulse in the
signal from the adapter card tells the monitor how fast to
actually run.  Recall the two pictures above? Only part of the
time required for raster-scanning a frame is used for displaying
viewable image (ie. your resolution).  9.1. Horizontal Sync:  By
previous definition, it takes HFL ticks to trace the a
horizontal scan line. Let's call the visible tick count (your
horizontal screen resolution) HR. Then Obviousl