Browse Prior Art Database

Self Powered Display Data Channel

IP.com Disclosure Number: IPCOM000122931D
Original Publication Date: 1998-Jan-01
Included in the Prior Art Database: 2005-Apr-04
Document File: 2 page(s) / 68K

Publishing Venue

IBM

Related People

Leaver, D: AUTHOR

Abstract

Display Data Channel (DDC) is a communications interface used specifically in personal computers. It consists of: 1. A IIC bus serial interface between Personal Computer and computer monitor. 2. A data table in the monitor.

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

Self Powered Display Data Channel

      Display Data Channel (DDC) is a communications interface used
specifically in personal computers.  It consists of:
  1.  A IIC bus serial interface between Personal Computer
       and computer monitor.
  2.  A data table in the monitor.

      The data table has information about Monitor make, model
number, serial number, supported video modes, white point, etc.  This
can be used for asset control as well as plug and play.

      The Personal Computer (PC) during booting requests the monitor
(via DDC) to send it the data it has stored in the data table.  With
this data, the PC knows the make, model and serial number of the
monitor attached.  It can select the optimum video mode to display
and also detect a change of monitor.  Without DDC data, the PC cannot
determine this and must output a default video mode.

      If the monitor is not powered during the time the data is
requested (within two seconds of the PC power up), then no data can
be supplied.  This causes the computer system to output an inferior
video mode.  This is extremely annoying to the user who may not
understand why this continues to happen.

      This problem was recognized during conception of DDC and a 5
volt supply made available on pin 9 of the PC video connector.
However, this is rarely used, most manufacturers preferring not to
add an extra  wire/pin in the already large interface cable.

      The power required by the DDC circuit within the monitor is
very small and is theoretically available from the H-Sync pulse.
This has been looked at before and discarded because not enough power
is guaranteed to be suppli...