IBASE Technology ET976 Guide

COM EXPRESS
CARRIER BOARD
DESIGN GUIDE
Version 1.0
(January 2022)

ii COM Express® Carrier Board Design Guide
Disclaimer
IBASE reserves the right to make changes and improvements to this document without prior notice. Every effort has
been made to ensure the information in the document is correct; however, IBASE does not guarantee this document
is error-free. IBASE assumes no liability for incidental or consequential damages arising from misapplication or
inability to use the information contained herein, nor for any infringements of rights of third parties, which may result
from its use.
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COM Express® Carrier Board Design Guide ii
i
TableofContents
Chapter 1 General Information ................................................................. 1
1.1ABOUT COM EXPRESS ........................................................................... 1
Chapter 2 COM Express Interfaces ............................................................... 2
2.1General Purpose PCIe Lanes .................................................................... 3
2.1.1Device Up / Device Down and PCIe Rx / Tx Coupling Capacitors ......... 3
2.1.2Schematic Examples .............................................................................. 4
2.1.3PCI Express Routing Considerations ..................................................... 7
2.2PEG (PCI Express Graphics) ..................................................................... 8
2.2.1Reference Schematics ......................................................................... 10
2.3Digital Display Interfaces ......................................................................... 11
2.3.1DisplayPort / HDMI / DVI .................................................................... 11
2.3.1.1Reference Schematic ......................................................................... 12
2.3.1.2Routing Considerations ...................................................................... 17
2.3.2SDVO ................................................................................................. 18
2.3.2.1Signal Definitions ............................................................................... 18
2.3.2.2Reference Schematics ....................................................................... 18
2.3.2.3Routing Considerations ...................................................................... 18
2.4LAN .......................................................................................................... 19
2.4.1Signal Definitions ............................................................................... 19
2.4.2Reference Schematics ....................................................................... 20
2.4.3Routing Considerations ...................................................................... 20
2.5USB Ports ................................................................................................ 21
2.5.1Signal Definitions ............................................................................... 21
2.5.2Reference Schematics ....................................................................... 22
2.5.3Routing Considerations ...................................................................... 22
2.6USB 3.0 .................................................................................................... 23
2.6.1Signal Definitions ............................................................................... 23
2.6.2Reference Schematics ....................................................................... 24
2.6.3Routing Considerations ...................................................................... 26
2.7SATA ........................................................................................................ 27
2.7.1Signal Definitions ............................................................................... 27
2.7.2Reference Schematic ......................................................................... 28
2.7.3Routing Considerations ...................................................................... 28

iv COM Express® Carrier Board Design Guide
2.8LVDS ........................................................................................................ 29
2.8.1Signal Definitions ............................................................................... 29
2.8.2Reference Schematics ....................................................................... 30
2.8.3Routing Considerations ...................................................................... 32
2.9Embedded DisplayPort (eDP) .................................................................. 33
2.9.1Signal Definitions ..................................................................................... 33
2.9.2Reference Schematics ............................................................................. 34
2.9.3Routing Considerations ............................................................................ 35
2.10VGA ......................................................................................................... 36
2.10.1Signal Definitions ............................................................................... 36
2.10.2VGA Reference Schematics .............................................................. 37
2.10.3Routing Considerations ...................................................................... 39
2.10.3.1RGB Analog Signals .................................................................... 39
2.10.3.2HSYNC and VSYNC Signals ....................................................... 39
2.10.3.3DDC Interface .............................................................................. 39
2.11Digital Audio Interfaces ............................................................................ 40
2.11.1Reference Schematics ....................................................................... 41
2.11.1.1High Definition Audio .......................................................................... 41
2.11.2Routing Considerations ...................................................................... 43
2.12LPC Bus – Low Pin Count Interface ........................................................ 44
2.12.1Signal Definition ................................................................................. 44
2.12.2LPC Bus Reference Schematics ........................................................ 45
2.12.2.1Super I/O ...................................................................................... 45
2.12.3Routing Considerations ...................................................................... 47
2.12.3.1General Signals ............................................................................ 47
2.13Serial Peripheral Interface Bus ................................................................ 48
2.13.1Signal Definition ................................................................................. 48
2.13.2SPI Reference Schematics ................................................................ 49
2.13.3Routing Considerations ...................................................................... 49
2.14General Purpose I2C Bus Interface ......................................................... 50
2.14.1Signal Definitions ............................................................................... 50
2.14.2Reference Schematics ....................................................................... 50
2.14.3Connectivity Considerations ............................................................... 5 0 
2.15System Management Bus (SMBus) ......................................................... 51
2.15.1Signal Definitions ............................................................................... 52
2.15.2Routing Considerations ...................................................................... 52

COM Express® Carrier Board Design Guide
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2.16General Purpose Serial Interface ............................................................. 53
2.16.1Signal Definitions ............................................................................... 53
2.16.2Reference Schematics ....................................................................... 54
2.16.2.1 General Purpose Serial Port Example ................................................ 54
2.16.3Routing Considerations ...................................................................... 56
2.17CAN Interface .......................................................................................... 56
2.17.1Signal Definitions ............................................................................... 56
2.17.2Reference Schematics ....................................................................... 57
2.17.3Routing Considerations ...................................................................... 58
2.18Miscellaneous Signals ............................................................................. 59
2.18.1Speaker Output .................................................................................. 60
2.18.2RTC Battery Implementation .............................................................. 61
2.18.3Power Management Signals .............................................................. 62
2.18.4Watchdog Timer ................................................................................. 65
2.18.5General Purpose Input/Output (GPIO) ............................................... 65
2.18.6Fan Connector ................................................................................... 66
2.18.7Thermal Interface ............................................................................... 67
2.19PCI Bus .................................................................................................... 68
2.19.1Signal Definitions ............................................................................... 68
2.19.2Reference Schematics ....................................................................... 70
2.20IDE and CompactFlash (PATA) ............................................................... 72
2.20.1Signal Definitions ............................................................................... 72
Chapter 3 Power and Reset .......................................................................... 74
3.1ATX Style Power Control ......................................................................... 75
Chapter 4 Carrier Board PCB Layout Guidelines ....................................... 78
4.1General .................................................................................................... 79
4.2PCB Stack-ups ......................................................................................... 79
4.3Trace Impedance Considerations ............................................................ 82
Chapter 5 Mechanical Considerations ........................................................ 83
5.1Form Factors ............................................................................................ 83
5.2Heatspreader ........................................................................................... 84
5.3COM Express Carrier Board .................................... 錯誤! 尚未定義書籤。
5.4COM Express Module and Heatsink ........................ 錯誤! 尚未定義書籤。

vi COM Express® Carrier Board Design Guide
5.5 COM Express Connector (Tyco) .............................. 錯誤! 尚未定義書籤。
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General Information
COM Express® Carrier Board Design Guide 1
1
Chapter 1
General Information
This design guide provides suggestions on designing IBASE COM-Express products
including carrier boards and systems. For other carrier board schematic guidelines
please refer to the full specification in the PICMG® COM Express® Carrier Board
Design Guide.
This design guide is not a specification and should not be your sole reference. The
guide is intended for electronics engineers and PCB layout engineers involved in the
design of the COM Express Modules Carrier Boards. The schematic examples in
this document are believed to be correct, however, no guarantee is given. The
examples shown here have been taken from the designs that were already tested.
For any questions that you may have in the design of carrier boards, please contact
IBASE sales representatives or engineers in your area.
1.1 ABOUT COM EXPRESS
COM Express is a highly integrated computer module that is integrated with the
CPU, memory and I/O functions including USB, audio, graphics and Ethernet, which
signals are mapped to two high-density, low-profile connectors at the bottom of the
module.
COM Express uses a mezzanine concept, with a module inserted onto customized
base boards. The module and base boards can be both upgraded to newer versions
and to earlier-designed compatible versions. Common applications for COM Express
modules are in various applications in the field of IoT, industrial automation, military,
gaming, medical and transportation.

2 COM Express® Carrier Board Design Guide
Chapter 2
COM Express Interfaces
The information provided in this chapter includes:
 General Purpose PCIe Lanes
 PEG (PCI Express Graphics)
 Digital Display Interfaces
 LAN
 USB Ports
 USB 3.0
 SATA
 LVDS
 Embedded DisplayPort (eDP)
 VGA
 Digital Audio Interfaces
 LPC Bus – Low Pin Count Interface
 Serial Peripheral Interface Bus
 General Purpose I2C Bus Interface
 System Management Bus (SMBus)
 General Purpose Serial Interface
 CAN Interface
 Miscellaneous Signals
 PCI Bus
 IDE and CompactFlash (PATA)

COM Express® Carrier Board Design Guide 3
2.1 General Purpose PCIe Lanes
2.1.1 Device Up / Device Down and PCIe Rx / Tx Coupling Capacitors
Figure 1: PCIe Rx Coupling Capacitors
The coupling caps for the Module PCIe TX lines are to be on the Module, as indicated in the COM
Express specification.

4 COM Express® Carrier Board Design Guide
2.1.2 Schematic Examples
Figure 2: PCI Express x1 Slot Example