Browse Prior Art Database

Advanced Monitor Mode Control

IP.com Disclosure Number: IPCOM000101854D
Original Publication Date: 1990-Sep-01
Included in the Prior Art Database: 2005-Mar-17
Document File: 3 page(s) / 88K

Publishing Venue

IBM

Related People

Gibbs, TK: AUTHOR [+2]

Abstract

A method of expanding personal computer (PC)-type monitor-mode control from four modes to eight is described.

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

Advanced Monitor Mode Control

       A method of expanding personal computer (PC)-type
monitor-mode control from four modes to eight is described.

      The scanning rates of a display are determided by its host
system.  The system must be able to communicate with the attached
display to define the required operating mode. Some PS/2* monitors
have four modes, but further modes may be desirable.  The present
system of mode selection is fully utilized and leaves no room for
expansion.  This disclosure describes a cost-effective method of
expanding mode control up to eight with minimum changes.  The result
is a flexible system that is totally retrospectively compatible.  No
additional complexity is required at the system unit or extra
connectors to the monitor.

      The present system for mode detection examines the polarity of
the horizontal and vertical synchronizing pulses.  Each is resolved
into either positive or negative levels.  These four states define
the four modes.  For modes 1 to 3 the vertical (field) sync pulse
duration is 63 us, while in mode 4 the pulse width is around 113 us.
This pulse width can be detected and become the third signal defining
the extra four modes.

      The important parameter of the vertical sync pulse is the time
between the end of active video and the leading edge of the pulse.
Since the vertical oscillator is an edge-triggered device, the width
of this pulse is of no value to a conventional monitor.  The width of
the pulse is not constrained by the PC other than that the maximum
length must be less than the total vertical blanking period.  In
generating new standards this pulse length can be defined to extend
control.  The pulse can be timed at the monitor and can be measured
to be less than or greater than 90 us. These two additional states
will expand the existing four modes to eight.  Table 1 shows the
eight possib...