Browse Prior Art Database

Improved Method of Monitor Identification And Mode Control

IP.com Disclosure Number: IPCOM000102087D
Original Publication Date: 1990-Oct-01
Included in the Prior Art Database: 2005-Mar-17
Document File: 3 page(s) / 105K

Publishing Venue

IBM

Related People

Morrish, AJ: AUTHOR

Abstract

The method disclosed in this article allows expansion of the existing PS/2* system unit/monitor interface without expanding the number of data lines. It remains compatible with contemporary software yet offers considerable expansion potential within the scope of future requirements. Additional hardware costs are low.

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This is the abbreviated version, containing approximately 52% of the total text.

Improved Method of Monitor Identification And Mode Control

       The method disclosed in this article allows expansion of
the existing PS/2* system unit/monitor interface without expanding
the number of data lines.  It remains compatible with contemporary
software yet offers considerable expansion potential within the scope
of future requirements. Additional hardware costs are low.

      The PS/2 display interface has the ability to:
a)   Select appropriate display formats in the monitor by sensing the
polarity of the two sync pulse signals giving four independent modes
of operation.
b)   Enable the system unit to identify the type of monitor by
reading the status of four ID bits which are connected to logic high
or low levels internal to the monitor allowing identification of 16
types of monitors.  Both sets of lines are becoming oversubscribed
with applications requiring additional modes of operation, and to
distinguish between monitors of similar types.  Any extension of this
system must be compatible with existing hardware and software.

      Extended ID System In the proposed extension, the system unit
is enhanced to have the ability to write to one or more of the ID
bits in addition to reading.  To prevent damage in the event of
connection to Oc there is a current limiting resistor in series with
the write line(s).  In the monitor the passive ID bit connections are
replaced with a small logic block that can reply to an interrogation
from the system unit via the ID bit lines.  This logic block is
desgined so that it is set to write the nominal monitor ID to the ID
lines by a power-on reset in order to be compatible with today's
system units.  A typical simple example of the system is shown in
Fig. 1, the monitor interface, and Fig. 2, that of the system unit.
Greater flexibility can be gained by more complex circuits based on
the same principle.

      Monitor ID Interface In Fig. 1, a low-cost CMOS input TTL
output inverter gate package is used.  This is chosen because of its
high input impedance, 50% switching thresholds, and low cost.  It is
TTL compatible; similar gates are at present used in the mode
decoders in existing PS/2 monitors.  The RC network Rl and C1 hold Q2
input high during power-up sufficiently long to set the latch system
of Q1 and Q2, in this case, at a low level output.  Levels are taken
from this latch to drive some or all of the other ID bits which, at
p...