Currently, video display technology is divided into analog type display devices (such as cathode ray tubes) and digital type display devices (such as liquid crystal display, or LCD, plasma screens, etc.), each of which must be driven by specific input signals in order to successfully display an image. For example, a typical analog system includes an analog source (such as a personal computer, DVD player, etc.) coupled directly to a display device (sometimes referred to as a video sink) by way of a communication link. The communication link typically takes the form of a cable (such as an analog VGA cable in the case of a PC, otherwise referred to as VGA DB15 cable) well known to those of skill in the art. For example, the VGA DB15 cable includes 15 pins, each of which is arranged to carry a specific signal.
One of the advantages of the VGA DB15 cable is the ubiquitous nature of the cable, due to the large and ever-expanding installed base. As long as the analog systems described above predominate, there is little incentive to migrate away from any other cable form than the VGA DB15.
However, in recent years, the exploding growth of digital systems has made the use of digital capable cables such as Digital Visual Interface (DVI) cable more desirable. It is well known that DVI is a digital interface standard created by the Digital Display Working Group (DDWG). Data are transmitted using the transition minimized differential signaling (TMDS) protocol, providing a digital signal from the PC's graphics subsystem to the display. DVI handles bandwidths in excess of 160 MHz and thus supports UXGA and HDTV with a single set of links.
Today's display interconnect landscape includes the VGA (analog) and DVI (digital) for desktop display interconnect applications as well as LVDS (digital) for internal connectivity applications within laptops and other all-in-one devices. Graphics IC vendors, display controller IC vendors, monitor manufacturers and PC OEMs as well as desktop PC consumers, to one degree or another, must factor interface choice into their design, product definition, manufacturing, marketing and purchase decisions. For example, if a consumer purchases a PC with an analog VGA interface then the consumer must either purchase an analog monitor or a digital monitor in which the analog video signal provided by the VGA interface has been digitized by way of an inline analog to digital converter (ADC) or an ADC built into the particular monitor.
Therefore, it would be desirable to have a simple enumeration method for regenerating a pixel clock from a link clock.