Browse Prior Art Database

DDC1 to DDC2B Power-Up

IP.com Disclosure Number: IPCOM000115127D
Original Publication Date: 1995-Mar-01
Included in the Prior Art Database: 2005-Mar-30
Document File: 2 page(s) / 65K

Publishing Venue

IBM

Related People

Dalgleish, SN: AUTHOR

Abstract

The Video Electronics Standards Association Display Data Channel Standard (VESA DDC) defines that any monitor/display should provide both DDC1 and DDC2 capability (minimum DDC2B). Monitors should power-up in DDC1 mode and change to DDC2 mode only after a valid high to low edge on SCL signal (driven by the host/system). VESA Display Data Channel (DDC) Proposal Version 1.0p, Rev 0.50 Section 4.1 DDC Level Selection (Display): "The display is always both DDC1 and DDC2 capable with DDC2 having the higher priority. The display shall start transmitting DDC1 signals whenever it is powered on and the vertical sync signal is applied to it from the host for the first time.

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

DDC1 to DDC2B Power-Up

      The Video Electronics Standards Association Display Data
Channel Standard (VESA DDC) defines that any monitor/display should
provide both DDC1 and DDC2 capability (minimum DDC2B).  Monitors
should power-up in DDC1 mode and change to DDC2 mode only after a
valid high to low edge on SCL signal (driven by the host/system).
VESA Display Data Channel (DDC) Proposal Version 1.0p, Rev 0.50
Section 4.1 DDC Level Selection (Display): "The display is always
both DDC1 and DDC2 capable with DDC2 having the higher priority.  The
display shall start transmitting DDC1 signals whenever it is powered
on and the vertical sync signal is applied to it from the host for
the first time.  The display shall switch to DDC2 as soon as it sees
a high to low transition on the clock line (SCL), indicating that
there are other DDC2 devices connected to the bus."

      Monitor/displays are an extremely electrically noisy
environment for digital circuitry, especially during power-up.  This
noisy environment means that a rogue/unwanted "glitch" or "edge" on
SCL could cause the DDC1/2 monitor/display to erroneously change from
DDC1 to DDC2 mode, especially during power-up.  The implications of
entering DDC2 mode erroneously are:
  1.  DDC1 Host/Systems - Fails to recognize that a DDC1/2 monitor is
       attached, resulting in a complete LOSS of DDC capability.
        The DDC monitor/display requires to be powered-down and
         subsequently repowered-up before DDC1 mode can possibly be
         re-entered.  Even this undesirable sequence may not be
possible,
         as the customer is unlikely to know that a failure has
occurred.
  2.  DDC2 Host/Systems - Potentially fails to reco...