XFree86 Video Timings HOWTO : Black Magic and Sync Pulses
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## 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:

### 9.2. Vertical Sync:

XFree86 Video Timings HOWTO : Black Magic and Sync Pulses
Previous: Computing Frame Sizes
Next: Horizontal Sync: