Preface<= /span>

Intellectual Property<= /span>

While every precaution= has been taken in the preparation of this standard, the Video Electronics Standards Association and its contributors assume no responsibility for errors or omissions, and make no warranties, expressed or implied, of functionality or suitability for any purpose.

Trademarks<= span style=3D'font-size:14.0pt;mso-bidi-font-size:10.0pt'>

All trademarks used wi= thin this document are the property of their respective owners. VESA, DDC, EDID,= and E-EDID trademarks of the Video Electronics Standard Association. I^{2C
is a trademark owned by Philips.}

Patents

VESA proposals and sta= ndards are adopted by the Video Electronics Standards Association without regard a= s to whether their adoption may involve any patents or articles, materials, or processes. Such adoption does not assume any liability to any patent owner,= nor does it assume any obligation whatsoever to parties adopting the proposals = or standards documents.

Support for this Stand= ard

Clarifications and application notes to support this standard may be written. To obtain the latest standard and any support documentation, contact VESA.

If you have a product, which incorporates CVT, you should ask the company that manufactured your product for assistance. If you are a manufacturer, VESA c= an assist you with any clarification you may require. All comments or reported errors should be submitted in writing to VESA using one of the following methods.

· Fax &n= bsp; : &= nbsp; 408-957 9277, direct this note to Technical Support at VESA

· e-mail: &nbs= p; support@vesa.org

· mail: = Technical Support

&= nbsp; &nbs= p; Video Electronics Standards Association

&nbs= p; &= nbsp; 860 Hillview Court, Suite 150

&nbs= p; &= nbsp; Milpitas, CA 95035

&nbs= p; &= nbsp;

= . 19

= 1.     Overview

1.1&= nbsp; Summary

This document details an equation-based method of creating timings. Rules for timing generation are al= so specified so as to control the number of possible formats in existence. Additionally, this document also specifies a way of creating Reduced Blanking timings for new display devices such as LCDs that don’t require as much Horizontal Blanking timing as traditional CRTs.

1.2&= nbsp; Background

The computer industry has, primarily due to the high degree of flexibility prov= ided by the modern continuous-frequency CRT display, traditionally employed a ve= ry wide range of display formats and timings even within a given individual system. This permits the syst= em to adapt the display “on the fly” to the requirements of various applications, and also permits the user to adapt the system to a wide range= of display-device formats, sizes, and technologies. However, to date, the development = of timing standards for these various combinations of formats and rates has not been done in any sort of coordinated manner – and so we have a number= of various standard formats which do not interoperate well, and timings which cannot all be precisely produced by any given graphics system.

VESA first attempted to address this problem through the release of the Generali= zed Timing Formula (GTF) Standard in 1996; GTF defined a process whereby a given display device and host system could algorithmically determine a timing whi= ch would permit both to work together, reducing the need for explicit timing specifications to cover all possible cases. The GTF method works well on= paper since it relies on being able to create a pixel frequency of infinite resolution. This, however, is= not practical for real world applications where clock generators have a finite resolution. It also does not = cater for an increasing market segment, such as “video in a window”, which requires the video timing to be precisely locked to an external image source.

Also, due to the increasing number of non-CRT, fixed-format display types in the market, there is a need for timing standards that specifically address the requirements of these technologies. CRT-compatible timings require higher pixel rates than would be requ= ired by these other display technologies due to large amount of blanking which is required for retrace. This, i= n most cases, represents wasted bandwidth and results in higher-than-needed clock rates.

In addressing these needs, though, it is important to keep in mind the fact th= at the computer graphics systems, which must produce video outputs to these specifications, are not infinitely flexible. In general, they cannot produce any arbitrary number of pixels per line, synthesize any given pixel clock exact= ly, and so forth. In addition, the problem of scaling information between different formats and rates says tha= t we should not simply generate timings and formats as independent entities. Some thought should be given to the interoperability and compatibility within the chosen set, as well as to the ability of the graphics hardware to produce the specified timing.

This standard represents an attempt to address these needs in a single, coordina= ted effort by developing a set of rules for generating timing. The goal being to create a method = by which display manufacturers and graphic hardware vendors can develop new products with enhanced compatibility and interoperability.

1.3&= nbsp; Standard Objectives

Previously the generation of new timing and form= ats has been done by hand and lagged the industry’s needs. This has caused confusion as new d= isplay devices or formats are introduced into the market with several different timings. The purpose of CVT i= s to define a method of creating timings so that new timings can be created simp= ly and easily. CVT provides a coordinated approach so that timing source generators and display devices k= now what the requirements for producing new timings will be and can provide for= ward compatibility to formats not yet conceived.

In addition, this standard also provides a way to generate timing with Reduced Blanking.&nbs= p; This enables newer display devices, such as LCDs, which don’t require as much blanking as CRTs, to reduce the pixel rate and use the transmission bandwidth from the source to the display more efficiently.

The long-term goal of CVT is to replace existing DMTs (Display Monitor Timings) and become the standard method for generating new timings. It will also ena= ble increased automation of creating published lists of DMTs that are generated using the CVT method.

1.4&= nbsp; Reference Documents

· VESA Enhanced Extended Display Identification Data Standard – E-EDID, Release A, Sept. 2, 1999

· VESA Enhanced Display Data Channel Standard - E-DDC, Version 1, Sep= t. 2, 1999

· VESA Generalized Timing Formula Standard - GTF, Version 1.0, Dec. 1= 8, 1996

· VESA and Industry Standards and Guidelines for Computer Display Mon= itor Timings – DMT, Version 1.0, Rev. 0.8, Sept. 17, 1998.

· VESA E-EDID Implementation Guide, Version 1.0, June 2, 2001

David Glen	ATI Technologies, Inc.	Jory Olson	InFocus
Joe Goodart	Dell Computer Corp.	Hiroshi Yamashita	International Display Tech.
Shiro Makino	Eizo Nanao Corporation	Keita Kitahama	NVIDIA Corp.
Graham Loveridge, Workgroup Leader	Genesis Microchip	Nozomu Kikuchi	Pioneer Corporation
		Steve Hasegawa	Sony
Jim Webb	Genesis Microchip	Joe Miseli	Sun Microsystems
Youichi Igarashi	Hitachi Ltd.	Don Chambers	Total Technologies Ltd.