Dvo Gmbus And Ddc Interface Considerations - Intel 855GME Design Manual

®
Intel 855GME Chipset and Intel
Integrated Graphics Display Port
6.5

DVO GMBUS and DDC Interface Considerations

The GMCH DVOB and/or DVOC port controls the video front-end devices via the GMBUS (I
interface. DDCADATA and DDCACLK shall be connected to the CRT connector. The GMBUS
shall be connected to the DVO device, as required by the specifications for those devices. The
protocol and bus may be used to configure registers in the TV encoder, TMDS transmitter, or any
other external DVI device. The GMCH also has an option to utilize the DDCPCLK and
DDCPDATA to collect EDID (Extended Display Identification) from a digital display panel.
Pull-ups (or pull-ups with the appropriate value derived from simulating the signal) typically
ranging from 2.2 k Ω to 10 k Ω are required on each of these signals.
The following GMCH signal groups list the five possible GMBUS pairs.
Table 56. GMBUS Pair Mapping and Options
Pair #
0
1
2
3
4
5
NOTE: MDDC pair is not available for use with the Extreme Graphics Driver.
NOTE: All GMBUS pairs may be optionally programmed to support any interface and is programmed through
the BMP utility.
When any of the GMBUS pairs (except DDCADATA/DDCACLK for CRT) are not used,
2.2 k-100 k Ω pull-up (or pull-ups with the appropriate value derived from simulating the signal)
resistors are required except for LCLKCTRLA/LCLKCTRLB GMBUS pair. This prevents the
GMCH DVOB interface from confusing noise on these lines for false cycles.
170
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6300ESB ICH Embedded Platform Design Guide
Buffer
Signal Name
Type
DDCADATA
DDC for Analog monitor (CRT)
3.3 V
connection
DDCACLK
LCLKCTRLA
For control of SSC clock generator
3.3 V
devices down on motherboard
LCLKCTRLB
DDCPDATA
DDC for Digital Display connection
3.3 V via the integrated LVDS display port
DDCPCLK
for support for EDID panel*
MDVIDATA
GMBUS control of DVI devices
1.5 V
(TMDS or TV encoder)
MDVICLK
MI2CDATA
GMBUS control of DVI devices
1.5 V
(TMDS or TV encoder)
MI2CCLK
MDDCDATA
DDC for Digital Display connection
1.5 V
via TMDS device
MDDCCLK
Description
This cannot be shared with
other DDC or I2C pairs due to
legacy monitor issues.
If SSC is not supported, then
may be used for DVOB or
DVOC GMBUS.
If EDID panels are not
supported, may optionally use
as GMBUS for DVOB or
DVOC.
May optionally use as GMBUS
for DVOB or DVOC.
May optionally use as GMBUS
for DVOB or DVOC.
May optionally use as GMBUS
for DVOB or DVOC.
2
C)
Notes