COM Express
COM Express, a computer-on-module 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, 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.
History
The COM Express standard was first released in 2005 by the PCI Industrial Computer Manufacturers Group 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 to allow additional flexibility to better serve the end application while maintaining compatibility within each module "Type."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. COM Express is an open standard.
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 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.Maximum available interfaces for the defined types:
| Type | Connectors | PCI Express lanes | PEG | PCI | IDE | SATA | LAN | Video | Serial | Other features | Note |
| 1 | AB | 6 | No | No | No | 4 | 1 | LVDS A & B, VGA | Legacy | ||
| 2 | AB & CD | 22 | Yes | Yes | 1 | 4 | 1 | LVDS A & B, VGA, PEG/SDVO | Legacy | ||
| 3 | AB & CD | 22 | Yes | Yes | No | 4 | 3 | LVDS A & B, VGA, PEG/SDVO | Legacy | ||
| 4 | AB & CD | 32 | Yes | No | 1 | 4 | 1 | LVDS A & B, VGA, PEG/SDVO | Legacy | ||
| 5 | AB & CD | 32 | Yes | No | No | 4 | 3 | LVDS A & B, VGA, PEG/SDVO | Legacy | ||
| 6 | AB & CD | 24 | Yes | No | No | 4 | 1 | LVDS A & B,VGA, 3 x DDI | 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 | 32 | Yes, for 16 lanes. | Yes | No | 2 | 1 + 4x 10G KR | - | 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 |
| 10 | AB | 4 | No | No | No | 2 | 1 | LVDS A only, DDI | 2 Serial COM, 1 optional CAN | USB 3.0 |
Option on previously allocated SATA2 and SATA3 pins. Implementor specific.
DDI can be adapted to DisplayPort, HDMI, DVI or SDVO in the carrier board.
Legend: PEG - PCI Express Graphics. Legacy - not recommended for new designs.
Size
The specification defines 4 module sizes:- Mini:
- Compact:
- Basic:
- Extended:
Specification
The current revision 3.0 was released in March 2017.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.
It also defines a carrier board eeprom to hold configuration information. This is also a separate an free available document