Kontron COMe Starterkit Eval T2 User Manual
Page 58
COM Express Interfaces
A Dual-mode source Module requires level shifters on the Carrier to convert the low-swing AC
coupled differential pairs from the video source to HDMI compliant current mode differential
outputs. The example schematics use a Chrontel CH7318C translator which supports data rates
up to 1.65GB/s per lane. FET based passive level translators can be used for lower data rates.
The DisplayPort AUX channel is configured as a DDC interface for HDMI. Further information on
pre-emphasis as well as output current trim capabilities of the CH7318C can be found in the
Chrontel datasheet.
See for more
information.
ESD clamping diodes D159, D160 and D161 protect the Module from external ESD events and
should be placed near the HDMI connector. The pin-out of the ESD clamp diodes allows for a
trace to run under the chip connector to two pins.
HDMI uses I2C signaling for the DDC. Resistors 1319 and 1322 provide the necessary pull-up.
The FETs U32 and U33 provide the Hot Plug Detect signal
The Carrier provides 5V power to the HDMI connector. A series diode (D72) should be used to
prevent back feeding of power in the event that the monitor is powered up when the Carrier is
powered down.
The HDMI Hot Plug Detect signal is buffered by two FETs U32 and U33 which prevent back
feeding of power from the display to the Module as well as level translation to 3.3V levels.
Note:
The reference schematics assume that the Module’s DDI ports are dual-source
capable – dual source indicates that the Module can output DisplayPort or
HDMI/DVI based on the DDC_AUX_SEL signal.
PICMG
®
COM Express
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Carrier Board Design Guide
Rev. 2.0 / December 6, 2013
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