Capes are expansion boards that plug in to the expansion connectors, P8 and P9, on the BeagleBone and have a specific pin usage. Capes are defined in the BeagleBone SRM document. Capes are specific to the BeagleBone subfamily and specifically do not include the BeagleBoard Classic or the BeagleBoard xM. Anyone can build a cape using the description in the SRM.
Note
For readers familiar with the microcontroller-based Arduino boards, capes are conceptually similar to a shield for Arduino boards.
As defined in the BeagleBone SRM, capes can be of any shape, but the location of the Ethernet RJ45 connector along with the location of the LED can dictate a specific cut-out pattern. Alternatively, extra tall connectors can be used to clear the Ethernet RJ45 connector. Up to four capes can be stacked using dual-sided connectors. A dual-sided connector is a through hole connector with male pins on one side to fit the expansion connectors P8 and P9, and a female socket on the other...