Kontron COMe Starterkit Eval T2 Bedienungsanleitung PDF herunterladen (Seite 152)

COM Express Interfaces

The clock trace from the COM Express Module to a PCI bus slot should be 2.5 inches shorter

because PCI cards are specified to have 2.5 inches of clock trace length on the card itself.

PCI clock signals should be routed as a single ended trace with a trace impedance of 55Ω. To

reduce EMI, a single ground referenced internal layer is recommended. The clock traces should

be separated as far as possible from other signal traces.

Refer to Section 6.6.1 'PCI Trace Routing Guidelines' on page 191 below and the 'PCI Local Bus

Specification Revision 2.3' to get more information about this subject.

Note: An approximate value for the signal propagation delay per trace length inch

can be calculated by using the following formula:

prop.

√

11.8

inch

' can be determined from the dielectric constant of the PCB that is used by

the following approximation. A typical value for the dielectric constant of an

FR4 PCB material is 4.2 < ε

< 4.5.

For stripline routing:

' =ε

For microstrip routing:

'=0.475 ε

+0.67 for 2.0< ε

<6.0

PICMG

COM Express

Carrier Board Design Guide Rev. 2.0 / December 6, 2013

152/218

1 2 ... 147 148 149 150 151 152 153 154 155 156 157 ... 217 218

Keine Kommentare

Kontron COMe Starterkit Eval T2 Bedienungsanleitung Seite 152