Programmable Dot Clock for Video Adapter
Original Publication Date: 1987-Apr-01
Included in the Prior Art Database: 2005-Feb-01
A programmable clock provides a wide range of frequencies for a video adapter, thereby permitting the adapter to be used with different types of video monitors. The dot clock in a video adapter is the fundamental timing signal that drives all the logic in the adapter. Typical adapters are designed with fixed frequency oscillators. Some adapters are designed with circuitry that can select, under program control, a frequency that is a binary division of a fixed frequency oscillator. Limitations of this technique are the extremely high frequencies involved which give rise to EMC problems, require high speed high current logic devices, and still do not give a wide selection of frequencies. An alternative to this approach is shown in the drawing.