Some of the bus lines are reserved or used for special signals. Be careful that expansion modules do not use signals on the HDRA and HDRB that clash with signals carried between the core module and baseboard.

Custom core modules cannot be added unless they have their own system bus and address space. That is, they must not use the bus signals on HDRA and HDRB. The module must have some dual-port memory, or some equivalent communication mechanism, in order to communicate with other modules. (Any additional custom core modules must operate in slave mode.)

The appropriate connector type and spacing must be used.

The new module must decode its own address space.

Keep the current drawn by the system below the limits.