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COM Express

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

COM Express, a computer-on-module (COM) form factor, is a highly integrated and compact computer that can be used in a design application much like an integrated circuit component. Each module 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, Internet of things, and general computing embedded applications.

History

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The COM Express standard was first released in 2005 by the PCI Industrial Computer Manufacturers Group (PICMG).[1] It defined five module types, each implementing different pinout configurations and feature sets on one or two 220-pin connectors. It also defined 2 module sizes (later expanded to 4) to serve more applications while maintaining compatibility within each module type.[2] COM Express is used in railway, industrial, and military applications. There are also efforts for a Rugged COM Express specification through VITA.

Types

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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.[3]

Maximum available interfaces for the defined types:

Type Connectors PCI Express lanes PEG PCI IDE SATA LAN Video Serial Other features Note
1 AB (Single) 6 No No No 4 1 LVDS A & B, VGA Legacy
2 AB & CD (Double) 22 Yes Yes 1 4 1 LVDS A & B, VGA, PEG/SDVO Legacy
3 AB & CD (Double) 22 Yes Yes No 4 3 LVDS A & B, VGA, PEG/SDVO Legacy
4 AB & CD (Double) 32 Yes No 1 4 1 LVDS A & B, VGA, PEG/SDVO Legacy
5 AB & CD (Double) 32 Yes No No 4 3 LVDS A & B, VGA, PEG/SDVO Legacy
6 AB & CD (Double) 24 Yes No No 4 1 LVDS A & B, VGA, 3 x DDI (*2) 2 TX/RX serial pairs with option to overlay CAN interface on 1 port 4x 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[3]
10 AB (Single) 4 No No No 2 1 LVDS A only (AB (Single) channel), DDI (*2) 2 Serial COM, 1 optional CAN USB 3.0 (*1)

(*1) Option on previously allocated SATA2 and SATA3 pins. Implementor specific. [4]

(*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. [5]

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

Size

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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

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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.[3] However, the COM Express Design Guide is free to download.

The original revision 1.0 was released July 10, 2005. Revision 3.0 (PICMG COM.0 R3.0) was released in March 2017.[6][3] 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 and free available document (EeeP R1.0).

See also

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References

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  1. ^ Jainandunsing, Kishan (September 9, 2004). "COM Express Tutorial" (PDF).
  2. ^ "COM Express subcommittee talks R2.1". PICMG Systems and Technology.
  3. ^ a b c d "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.
  4. ^ https://www.kontron.com/en/products/boards-standard-form-factors/com-express/c90452[bare URL PDF]
  5. ^ http://picmg.org//wp-content/uploads/PICMG_COMDG_2.0-RELEASED-2013-12-061.pdf [bare URL PDF]
  6. ^ "congatec welcomes official release of the COM Express 3.0 specification". congatec. April 13, 2017. Retrieved June 29, 2018.
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