Browse Prior Art Database

Automatic VGA-8 Mode Detection Method

IP.com Disclosure Number: IPCOM000112795D
Original Publication Date: 1994-Jun-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 2 page(s) / 70K

Publishing Venue

IBM

Related People

Nishimura, H: AUTHOR [+3]

Abstract

This article describes an Automatic VGA-8 mode detection method. This method is effective to detect the VGA-8 mode from VGA analog interface signals. No modification is required to a conventional VGA analog interface.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 56% of the total text.

Automatic VGA-8 Mode Detection Method

      This article describes an Automatic VGA-8 mode detection
method.  This method is effective to detect the VGA-8 mode from VGA
analog interface signals.  No modification is required to a
conventional VGA analog interface.

      Several screen modes of IBM Video Graphics Array (VGA) in IBM
Personal Computer compatible systems are provided by a video BIOS
program (VGA-BIOS modes).  On the other hand, VGA-8 is a special
screen mode which is not provided by the video BIOS program.  There
are two types of VGA-8 modes which are commonly used.  Since the
VGA-8 mode has different register settings from VGA-BIOS mode, the
number of the dots, which are contained in one scan line, are
different between the VGA-8 modes and VGA-BIOS modes.  Among the flat
panel monitors, which have the analog video interface, the
Phase-Locked Loop (PLL) is a popular technique for generating a dot
clock from dividing the Hsync period by a total number of dots in one
scan line in the monitor.  Therefore, the VGA-8 mode must be
distinguished from the VGA-BIOS mode in order to get the correct
frequency of the dot clock.

      The table in Fig. 1 shows a comparison of Hsync timing between
two types of VGA-8 modes and a VGA-BIOS mode.  This method detects
the difference of Hsync pulse widths between the VGA-8 modes and
VGA-BIOS mode.

      The Block Diagram in Fig. 2 shows an example of implementation,
which uses a clock from a free-run osci...