Browse Prior Art Database

Liquid Crystal Display Compatibility with 80COL VGA Software

IP.com Disclosure Number: IPCOM000105755D
Original Publication Date: 1993-Sep-01
Included in the Prior Art Database: 2005-Mar-20
Document File: 4 page(s) / 105K

Publishing Venue

IBM

Related People

Beanlands, P: AUTHOR [+3]

Abstract

Described is a mechanism which permits 640-pel Liquid Crystal Displays (LCDs) to be used with existing Video Graphics Application (VGA) adapters and software in 720-pel modes using hardware window techniques to scroll left to right. Provided is compatibility with existing software using 720-pel text modes and 360-pel graphics modes without degrading image quality. Included is LCD attachability to existing HW-Microcode designs without user interaction or loading special software.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Liquid Crystal Display Compatibility with 80COL VGA Software

      Described is a mechanism which permits 640-pel Liquid Crystal
Displays (LCDs) to be used with existing Video Graphics Application
(VGA) adapters and software in 720-pel modes using hardware window
techniques to scroll left to right.  Provided is compatibility with
existing software using 720-pel text modes and 360-pel graphics modes
without degrading image quality.   Included is LCD attachability to
existing HW-Microcode designs without user interaction or loading
special software.

      A VGA display adapter may be programmed into one of many modes,
each characterized by the pels/line and lines/frame.  The pels/line
can be selected as 320, 360 A4, 640 or 720 whilst the lines/frame can
be selected as 200, 350, 400 or 480.  This range of
"addressabilities" provides difficulties for LCDs which have largely
standardized on 640 pels by 480 lines.  Refer to Appendix for
background prior art.  Known techniques for resolving the vertical
mismatch between 200/350/400 lines and 480 lines use a combination of
centering and selective and/or full line replication which are
adequate.  The mismatch between 320 pels and 640 pels is accommodated
simply by pel replication, but the mismatch between 360/720 pels and
640 pels presents a major obstacle to the adoption of LCDs.
Disclosed is a simple effective solution that does not degrade image
quality.

      Proposed is a 640-pel-wide window into the 720-pel-wide image.
The default start point of the window should be pel 0 (i.e., an
offset of zero) but the start point may be made user-adjustable to
allow the window to be moved over the image width; therefore, an
offset adjustment range of 0 to 80 pels is required.  A simpler
implementation results if the user is provided with control which
sets the offset either 0 to 80, this permits either 640 view from the
start of the 720-pel line or a 640-pel view to the end of the 720-pel
line.

      This solution makes use of the fact that most of the newer
applications are using modes with 640 pels/line and therefore match
the addressability of LCDs.  For backwards compatibility, it is
necessary to provide some support for the older applications, POST
and DOS command line work which use modes with 720 pels/line, but
since these rarely use the last 9 characters on a row the
disadvantages of a 640-pel windo...