Mechanics for CompactPCI Plus: A comparison with familiar architectures such as VPX and MicroTCA

Version 1

    Author: Andreas Lenkisch, Principal Engineer for Backplanes, Schroff GmbH


    CompactPCI Plus is a new working group within the PCI Industrial Computer Manufacturers Group (PICMG) that defines a successor architecture for the CompactPCI bus.


    Emphasis in the development of the new architecture has been placed on retaining the CompactPCI ecosystem. However, this requires consideration not only of hardware but also of soft factors such as the knowledge and experience of technicians and may represent a high value in commercial terms. The members of the standards committee have deliberately opted for the familiar 19-inch technology. This allows, mechanically speaking, both 'old' parallel boards and new serial boards to operate in ideal conditions, side by side in the same chassis (Fig. 1). Additionally the board width is 4 HP (horizontal pitch) or 20.32 mm and the PCB is located in the same position. Thus there is no change whatsoever to the front panels (Fig. 2). Bolting positions and cut-outs for connectors are created by the same familiar rules. The IEEE 1101.10 extractor handle with microswitch for hot-swap, the board format of 160 mm x 100 mm or 233.35 mm and the fixing holes also remain as before (Fig. 3).

    The only change relates to the connector and its associated footprint and the connector-side hole for rear covers, while on the other hand the user benefits from higher data transfer rates and more flexibility in the system architecture. 


    VITA 46 VPX is also based on 19-inch technology and is used increasingly in military applications. VPX supports various high-speed interfaces, but not simultaneously. For this VPX defines boards and slot spacings for the different environmental conditions of air cooling through conduction cooling to direct liquid cooling of hot-spots on the board, which can dissipate up to about 450 watts.


    MicroTCA, on the other hand, uses a special new mechanical system, and so a soft migration such as CPCI Plus allows is considerably more problematic. However, its extensive shelf management makes hot-swap child's play: functionality and power and cooling requirements are checked before the board is powered up. Remote maintenance is implemented in the shelf management.

    MicroTCA likewise supports a wide variety of high-speed interfaces, which results in restrictions on simultaneous availability in the system.


    It can thus be seen CPCI Plus is the best suited to gearing existing PCI and CPCI applications up for the future.