= VESA^Ò = ; &n= bsp; = ; &n= bsp; = ; &n= bsp; = ; GTFÔ Standard=

Video Electronics Standards Association

860 Hillview Court, Suite 150 = &nb= sp; = &nb= sp; = &nb= sp; = Tel: (408) 957-9270

Milpitas, CA 95035 = &nb= sp; = &nb= sp; = &nb= sp; = Fax: (408) 957-9277

Generalized Timing For= mula Standard

Version: 1.1=

<= /o:p>

September 2,= 1999

Purpose

The VESA Generalized T= iming Formula is a standard method for generating general-purpose display timings. While bringing standardization, it does not restrict the market to fixed, p= re-defined formats or refresh rates, and thus allows differentiation within a standard= ized environment.

Summary

&nb= sp;

VESA has defined a sta= ndard method by which new formats and timings can be generated. This will allow m= uch greater flexibility in the choice of refresh rates and pixel formats than currently available with existing discrete monitor timings. GTF describes a computational method that will provide standardization, and yet also enable= new features, such as user defined image resolution and low-cost, automatic self-alignment of display devices, to be added to graphics systems and monitors,

Version 1.1 explains t= he usage of GTF parameters for a Secondary GTF curve; a concept called “Secondary GTF”.

Intellectual Property

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

Trademarks

All trademarks used within this document are the property of their respective owners. VESA is a registered trademark of the Video Electronics Standards Association.

Patents<= /o:p>

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

Support<= /o:p>

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 that incorporates GTF^TM, you should ask the company that manufactured your product for assistance. If you are a manufacturer, VESA can assist you with any clarification you may require. All comments or reported errors sh= ould be submitted in writing to VESA using one of the following methods.

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

<= span style=3D'font-size:11.0pt;mso-bidi-font-size:10.0pt;font-family:Symbol; mso-fareast-font-family:Symbol;mso-bidi-font-family:Symbol'>· Email: = ; support@vesa.org

· Mail: = Technical Support

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

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

= Milpitas, CA 95035

Acknowledgments

This specification would not have been possible without the valuable contributions and support from the following members of the GTF work group:

Andy Morrish (GTF Work Group Leader) National Semiconductor

Dave Eagle = &nb= sp; = &nb= sp; IBM

Ricky Jackson&nb= sp; = &nb= sp; IBM<= o:p>

Hans van der Ven &n= bsp; = ; Panasonic

Bob Myers &= nbsp; He= wlett-Packard

Anders Frisk &nb= sp; = &nb= sp; = ICL

Tom Ryan &n= bsp; = ; &n= bsp; = ; SciTech

Kendall Bennett = &nb= sp; SciTech

Joe Goodart = Compaq

Paul Doyle <= span style=3D'mso-tab-count:2'> &= nbsp; Sony

Version 1.1

Anders Frisk (GTF Document editor, work group leader) Nokia

Hans van der Ven &n= bsp; = ; Panasonic

Joe Goodart = Dell

Alain d’Hautecourt &= nbsp; &nbs= p; ViewSonic

GTF EXCEL^TM SPREADSHEET

As part of this standard, a companion EXCEL^TM V4.0 spreadsheet is available from = the VESA FTP site (GTF_V1R1.XLS), or from the VESA office. This spreadsheet illustrates the GTF method and allows manual computation of timing paramete= rs and demonstration of the computation method. This written specification documents the mathematical methods behind the spreadsheet in order to demonstrate how GTF can be programmed into software.

In case of any confusion or dispute regarding interpretation or calculation of= any of the GTF variables in any implementation, the released version of GTF spr= eadsheet shall be used as the definitive calculation method to demonstrate correct computation of the parameters.

REVISION HISTORY

Version 1.0 Revision 1.0, December 8, 1996

Initial release of GTF Standard

Version 1.1

Secondary GTF curve concept defined.<= /p>

TABLE OF CONTENTS=

Intellectual Property..........= ...........................................................................= 2

GTF EXCEL^TM SPREADSHEET.........................= .......................................................... = PAGEREF _Toc472477239 \h = 3

REVISION HISTORY..........................................= ............................................................ = 3

1. INTRODUCTION.................................................................= ....................................... 5

2 TERMS AND DEFINITIONS= ..........................................= ............................................ 6

2.1 Timing Parameters...................= .......................................................................... = 6

2.2 Sync Pulse Position.................= .......................................................................... = 7

2.3 Sync Pulse Polarity.................= ........................................................................ 7

2.4 Basic Horizontal Blanking Duty Cycle Formula......................... 8

2.5 Accuracy of Timing Parameters.......= ..................................................... 11

2.6 Extended Horizontal Blanking Formula= ........................................ 11

3 DEFAULT PARAMETER VAL= UES..........................................= ............................. 14

4 SYSTEM VARIABLES.................................................................= ............................ 15

5 &nb= sp; COMMUNICATING GTF COMPLIANCE THROUGH DDC/EDID.....= ......... 16

5.1. Definition of GTF-Compliant Monitors and Graphics Systems 16

5.3 GTF System Driver with GTF-Compliant Monitors......................... 16

5.4 GTF System Driver with Non-GTF DDC Monitors.............................. 16

5.5 GTF System Driver with User Defined Limits for Non-GTF Monitors 17

5.6 Summary of Monitor Default GTF Compliance.............................. 18

6 Secondary GTF.........= ...........................................................................= ................ 18

7 COMPUTATION OF TIMING PARAMETERS..........................................= ......... 19

7.1 Flow Chart of GTF Method............= .............................................................. 19

7.2 Rounding Definition.................= ..................................................................... 21

7.3 Using Vertical Refresh Frequency to Find Stage 1 Parameters &= nbsp; 21

7.5 Using Pixel Clock Frequency to Find Stage 1 Parameters..... 24

7.6 Using Stage 1 Parameters to Derive Stage 2 Parameters........ 26

APPENDIX A..........................................= ........................................................................ 30

FIGURES AND TABLES

Figure 1: Sync Pulse Timing Definitions..........................................= ............ 7

Figure 2: Basic Horizon= tal Duty Cycle Curve....................= .................. 10

Figure 3: Blanking Duty= Cycle Curves with Variations in K...... 12

Figure 4: Exam= ples of Variations in K, J, C and M.........................= .......... 13

Figure 5: The GTF Calculation..............................................................= ........... 20

Tables 1a and 1b: GTF Sync Polarities.......................................................... 8

Table 2: Definition of [I/P PARAMETER].......................................................... 15

Table 3: Summary of Monitor Default GTF Compliance.................. PAGEREF _Toc466572353 \h 18

1.&nb= sp; INTRODUCTION

GTF is a standard method for generating general-purpose display timings. While bringing standardization, it does not restrict the market to fixed, pre-defined formats or refresh rates and therefore allows differentiation within a standardized environment.

GTF is intended as a tool to be used by all part= ies concerned with video signal generation. Video graphics software drivers sho= uld utilize the GTF method to generate timing parameters for any new, previously unspecified video modes, either spontaneously within the PC from a set of system inputs, or in pre-defined and stored tables. Video graphic generation hardware should use and be compatible with the GTF method for definition of= any new modes of operation. Monitor designs should use the GTF method to determ= ine how to interpolate for new unrecognized timings, and consequently set image size and geometry parameters.

A principle objective of GTF is to allow predict= able timing parameters to be derived from minimal information. Using GTF, it is = possible to construct a complete set of timing parameters given the following basic information:

&nbs= p; 1) Pixel format (e.g. 800x600)

&nbs= p; 2) Whether or not overscan borders are required

&nbs= p; 3) Whether interlace is required

&nbs= p; 4) ONE of the following:

&= nbsp; Vertical refresh rate required

= or: Horizontal frequency required

= or: Pixel clock required

Using any one of the three options in (4) above,= the same timing parameters will result from GTF. This allows the calculation to= be ‘driven’ by intelligent system software to obtain best overall system performance, especially in conjunction with plug and play peripherals that can communicate the hardware capabilities. For example, knowing the limitations of a CRT display in vertical and horizontal scan frequencies, t= he maximum pixel clock rate of a graphics card, the desired vertical refresh r= ate of a User and the pixel format from an application, new system software can generate a new timing to meet the constraints of the hardware. Most importa= ntly, the GTF method also allows the possibility for displays to predict where the image may fall, and thus enables the possibility of automatic image set up = for any new mode.

A further objective is to minimize compatibility= problems that frequently result when graphics cards generate unique timings or cannot meet the exact timing parameters of standard formats. GTF provides a means = for graphics cards to generate these unique timings based around default timing characteristics that can be supported by most monitors. <= /p>

Another use of GTF is to enable new timing parameters to be generated for displays running at a constant horizontal sc= an frequency, potentially allowing simplified and lower-cost display designs. = This will also result in maximized vertical refresh rates, which is generally se= en as an ergonomic advantage.

In order to minimize the amount of information required at time of computation, and also to ensure basic standardization and compatibility in formats that = are produced, it is necessary to standardize the values of all other variables = that influence the calculation of timing parameters. In this specification, a standard definition and default value is given to each of these variables, in addition = to a standard method of timing parameter computation.

The GTF standard can be used with any pixel clock reference frequency, and will provide timings within the hardware constraints of this and other system parameters. However, it is ex= pected that some applications will continue to require specific discrete timing standards, as in the case of timings intended to be compatible with video or other systems. In order to pe= rmit such timings to be produced as precisely as possible, and to increase the <= o:p>

likelihood that controllers from different manufacturers will produce identical timings using either GTF or current and future discrete timings, VESA recommends th= at the fixed reference frequency (i.e. typically the fixed crystal reference used by the video phase locked oscillator for subsequent programm= able pixel clock synthesis) be one selected from the N x 2.25MHz family of rates. This set has been sele= cted for its compatibility with worldwide video timing standards, and will also = be used wherever possible in future Discrete Monitor Timing (DMT) standards produced by VESA. While this = is a recommendation, it should be noted that use of a reference from this partic= ular set is not a requirement for compliance to the VESA GTF standard.

Secondary GTF

Secondary GTF is a method for using the generalized timing formula to describe two separate functions that describe the relationship between the monitor timing signals. Both functions use the same formula, but with different parameter values. By using the default parameter values as defined in this document y= ou produce the default GTF curve. This curve describes the relationship between horizontal frequency and blanking time. The default GTF curve is suitable f= or most CRT monitors, however, there are monitor designs that can work with sh= orter blanking times than what the default GTF describes. The second GTF curve ca= n be used to describe the relation between timing signals when the monitor is operating in a mode with reduced blanking.

2 TERMS AND DEFIN= ITIONS

2.1 Timing Parame= ters<= /span>

Several different sync formats are used by display systems, including separate sync= s, composite syncs and sync-on- green. GTF has been formulated for optimum compatibility. In addition, careful consideration has been given to the cho= ice of sync width and positioning relative to the video to ensure best operation with the majority of present day display technology.

The following definitions are used within this specification to describe the important timing intervals (see figure 1):

Addressable Video (t_video)

The period during which active image video information is transmitted.

Margin (t_margin)

The period during which background colored border maybe displayed in order to a= llow the CRT image to extend beyond the limits of the surrounding bezel on overs= can type monitors. Typically, the margin period cannot be addressed on an individual pixel basis by the image buffer. On most non-overscan type syste= ms, the margin period is zero.

Blanking (t_blank)

The period between the end of one l= ine (horizontal) or frame (vertical) of the video and margin period, and the st= art of the next line or frame of video.

Sync pulse width (t_sync)

The period of the active sync pulse.

Front porch (t_fp)

The period between the end of one line (horizontal) or frame (vertical) of the video and margin period, and the start of the sync pulse.=

Back porch (t_bp)

The period between the end of the sync pulse and the start of the next line (horizontal) or frame (vertical) of the following video and margin period.<= o:p>