Browse Prior Art Database

Video Gate Array Programming for Flexible Screen Sizes

IP.com Disclosure Number: IPCOM000116264D
Original Publication Date: 1995-Aug-01
Included in the Prior Art Database: 2005-Mar-30
Document File: 2 page(s) / 70K

Publishing Venue

IBM

Related People

Dobkin, RJ: AUTHOR

Abstract

Disclosed is a method, or algorithm, for programming a Video Gate Array (VGA) display adapter so that arbitrary screen dimensions can be used by an application program. When this method is used, displayed information is automatically centered, and the image area is maximized, with an application no longer being limited by a requirement to use a small set of standard modes to display full screen output. This method of programming modifies the Cathode Ray Tube (CRT) controller registers to account for the dimensional differences between a standard mode and a mode with arbitrary dimensions. For example, the standard 80-column by 25-row text mode can be modified to provide a 70x30 mode.

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Video Gate Array Programming for Flexible Screen Sizes

      Disclosed is a method, or algorithm, for programming a Video
Gate Array (VGA) display adapter so that arbitrary screen dimensions
can be used by an application program.  When this method is used,
displayed information is automatically centered, and the image area
is maximized, with an application no longer being limited by a
requirement to use a small set of standard modes to display full
screen output.  This method of programming modifies the Cathode Ray
Tube (CRT) controller registers to account for the dimensional
differences between a standard mode and a mode with arbitrary
dimensions.  For example, the standard 80-column by 25-row text mode
can be modified to provide a 70x30 mode.

      In a first step of the programming method, a suitable standard
mode is programmed, having a horizontal resolution as close as
possible to, but not less than, the desired horizontal resolution.
For a graphics mode, a standard mode is chosen with a vertical
resolution as close as possible to, but not less than, the desired
vertical resolution.

      In a second step of the programming method, the horizontal
registers of the VGA CRT controller are modified if the desired
horizontal resolution differs from that of the standard mode.  The
VGA offset register is programmed with the new, desired horizontal
resolution.  A horizontal active difference is obtained as the
difference in horizontal resolution between the standard mode and the
desired mode.  The horizontal border difference, or difference in
border sizes between the modes, is obtained by dividing the
horizontal active difference by two, centering the new mode.  The VGA
horizontal display end register is...