COM Express
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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
[edit]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
[edit]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
[edit]The specification defines 4 module sizes:
- 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
[edit]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
[edit]- ETX
- XTX
- Qseven
- Smart Mobility Architecture (SMARC)
- COM-HPC (working group within PICMG)
References
[edit]- ^ Jainandunsing, Kishan (September 9, 2004). "COM Express Tutorial" (PDF).
- ^ "COM Express subcommittee talks R2.1". PICMG Systems and Technology.
- ^ 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.
- ^ https://www.kontron.com/en/products/boards-standard-form-factors/com-express/c90452[bare URL PDF]
- ^ http://picmg.org//wp-content/uploads/PICMG_COMDG_2.0-RELEASED-2013-12-061.pdf [bare URL PDF]
- ^ "congatec welcomes official release of the COM Express 3.0 specification". congatec. April 13, 2017. Retrieved June 29, 2018.
External links
[edit]
- PICMG website
- The Economics and use of COM Express in Embedded Applications
- COM Express Carrier Design Guide - Guidelines for designing COM Express Carrier Boards
- Purchase specification (scroll down to "PICMG COM.0 R3.0")
- Free available short for specification COM.0 R3.0
- Free available Embedded API Specification EAPI R1.0
- Free available Embedded EEPROM Specification EeeP R1.0
- COM Express Plug-and-Play Initiative
- COM Express: Scalability and flexibility for UAS sensor processing
- COM-HPC preview