Kontron COMe Starterkit Eval T2 - Manual (Page 65)

COM Express Interfaces
The Digital Video Interface (DVI) is based on the differential signaling method TDMS. To achieve
the full performance and reliability of DVI, the TDMS differential signals between the SDVO to
DVI transmitter and the DVI connector have to be routed in pairs with a differential impedance of
100Ω. The length of the differential signals must be kept as close to the same as possible. The
maximum length difference must not exceed 100mils for any of the pairs relative to each other.
Spacing between the differential pair traces should be more than 2x the trace width to reduce
trace-to-trace couplings. For example, having wider gaps between differential pair DVI traces will
minimize noise coupling. It is also strongly advised that ground not be placed adjacent to the DVI
traces on the same layer. There should be a minimum distance of 30mils between the DVI trace
and any ground on the same layer. For more information, refer to the layout and routing
considerations as specified by the manufacturer of the SDVO to DVI transmitter.
SDVO Option – PEG Lane Reversal
If Module pin D54 PEG_LANE_RV# is strapped low to untwist a bowtie on the PEGx16 lines to
an x16 slot, then an ADD2 card used in this slot must be a reverse pin-out ADD2 card.
Reverse pin-out ADD2 cards are designated ADD2-R.
If the SDVO device is “down” on the Carrier Board, then the PEG_LANE_REV# pin has no effect
because SDVO lines are not reversed on the chipset – only PCIe x16 lines are.
Please see the Lane Reversal caution at Section 2.4.4.2. 'Lane Reversal' on page 53 above.
PICMG ® COM Express ® Carrier Board Design Guide Rev. 2.0 / December 6, 2013
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