COM Express

COM Express, a computer-on-module (COM) form factor, is a highly integrated and compact PC that can be used in a design application much like an integrated circuit component. Each COM Express Module COM integrates core CPU and memory functionality, the common I/O of a PC/AT, USB, audio, graphics (PEG), and Ethernet. All I/O signals are mapped to two high density, low profile connectors on the bottom side of the module. COM Express employs a mezzanine-based approach. The COM modules plug into a baseboard that is typically customized to the application. Over time, the COM Express mezzanine modules can be upgraded to newer, backwards-compatible versions. COM Express is commonly used in Industrial, Military/Aerospace, Gaming, Medical, Transportation, IoT, and General Computing embedded applications.

COM Express Type 6 Module VIA COMe-8X92 with VIA Nano X2
COM Express Carrier Board

History

The COM Express standard was first released in 2005[1] by the PCI Industrial Computer Manufacturers Group (PICMG)[2] and it sought to provide standardized module interfaces for several different target applications. It did so by defining five different module "Types" each implementing different pinout configurations and feature sets on one or two 220-pin connectors. In that way, COM Express is a standard of multiple standards. It also defined 2 module sizes (later expanded to 4) to allow additional flexibility to better serve the end application while maintaining compatibility within each module "Type." [3] The COM Express form factor is used in many Railway, Industrial, and Military applications. There are also efforts for a Rugged COM Express specification in the works through VITA (vita.com). COM Express is an open standard.[4]

Types

There are 8 different pin outs defined in the specification. The most commonly used pin outs are Type 6 and Type 10. The latest pin-out added in revision 3.0 of the COM Express specification (available from www.picmg.org) is Type 7. The Type 7 provides up to four 10 GbE interfaces and up to 32 PCIe lanes, making COM Express 3.0 appropriate for data center, server, and high-bandwidth video applications. COM Express Rev 3.0 removed legacy Type 1, Type 2, Type 3, Type 4, and Type 5, recommending that new designs should use Type 6, 7 or 10. [5]

Maximum available interfaces for the defined types:

TypeConnectorsPCI Express lanesPEGPCIIDESATALANVideoSerialOther features Note
1AB (Single)6NoNoNo41LVDS A & B, VGA Legacy
2AB & CD (Double)22YesYes141LVDS A & B, VGA, PEG/SDVO Legacy
3AB & CD (Double)22YesYesNo43LVDS A & B, VGA, PEG/SDVO Legacy
4AB & CD (Double)32YesNo141LVDS A & B, VGA, PEG/SDVO Legacy
5AB & CD (Double)32YesNoNo43LVDS A & B, VGA, PEG/SDVO Legacy
6AB & CD (Double)24YesNoNo41LVDS A & B,VGA, 3 x DDI (*2)2 TX/RX serial pairs with option to overlay CAN interface on 1 port4x USB 3.0

8x USB 2.0
7 AB & CD (Double) 32 Yes, for 16 lanes. Yes No 2 1 + 4x 10G KR None 2 TX/RX serial pairs with option to overlay CAN interface on 1 port 4x USB 3.0

4x USB 3.0

 Added in Rev 3.0[5]
10AB (Single)4NoNoNo21LVDS A only (AB (Single) channel), DDI (*2)2 Serial COM, 1 optional CANUSB 3.0 (*1)

(*1) Option on previously allocated SATA2 and SATA3 pins. Implementor specific. [6]

(*2) DDI can be adapted to DisplayPort, HDMI, DVI or SDVO (legacy, no longer supported for types 6, 7 and 10) in the carrier board. [7]

Legend: PEG - PCI Express Graphics. Legacy - not recommended for new designs.

Size

The specification defines 4 module sizes:

COM Express has 4 form factors. See the PICMG COM Express specification for carrier board mounting positions.
  • Mini: 55 × 84 mm (2.2 × 3.3 in)
  • Compact: 95 × 95 mm (3.7 × 3.7 in)
  • Basic: 95 × 125 mm (3.7 × 4.9 in)
  • Extended: 110 × 155 mm (4.3 × 6.1 in)

Specification

The COM Express specification is hosted by PICMG. It is not freely available but a paper copy may be purchased for $150USD from the PICMG website.[5] However, the COM Express Design Guide is free to download.[4]

The current revision 3.0 (PICMG COM.0 R3.0) was released in March 2017.[8][5]The original revision 1.0 was released July 10, 2005.

COM Express also specifies an API to control embedded functionalities like watchdog timer or I2C. This is a separate document which is freely available (EAPI 1.0).

It also defines a carrier board eeprom to hold configuration information. This is also a separate an free available document (EeeP R1.0)

See also

References
  1. Jainandunsing, Kishan (September 9, 2004). "COM Express Tutorial" (PDF).
  2. "PICMG Open Modular Computing Standards". PICMG. Retrieved June 29, 2018.
  3. "COM Express subcommittee talks R2.1". PICMG Systems and Technology.
  4. "COM Express® Overview". PCIMG. Retrieved June 29, 2018.
  5. "COM Express Module Base Specification Revision 3.0" (PDF). PCIMG. March 31, 2017. Archived from the original (PDF) on July 2, 2018. Retrieved July 2, 2018.
  6. http://www.kontron.com/resources/collateral/white_papers/whitepaper_comexpresscom.0rev.2.0_en.pdf
  7. http://picmg.org//wp-content/uploads/PICMG_COMDG_2.0-RELEASED-2013-12-061.pdf
  8. "congatec welcomes official release of the COM Express 3.0 specification". congatec. April 13, 2017. Retrieved June 29, 2018.
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