LONDON PICMG has published a free COM Express Design Guide. The documents was created by a special PICMG subcommittee and provides information for designing a custom system carrier board for COM Express Modules.
The guide includes reference schematics for the external circuitry required to implement the various COM Express peripheral functions, explains how to extend the supported buses, and how to add additional peripherals and expansion slots to a COM Express-based system.
The guide contains additional information but does not replace the PICMG COM Express specification.
When used with the latest COM Express specification and the Module vendors' product manuals, the design guide should simplify design effort and help improve the interoperability of a customer's unique carrier board with other computer modules available from various PICMG members.
The document can be download from the PICMG Europe website.