The evolution of CompactPCI Serial

2CompactPCI Serial promises to be as successful as its parallel cousin, CompactPCI. This new specification combines the advantages of traditional CPCI with the latest high-speed data transfer rate technologies. Though CPCI Serial is not fully backward compatible, a path for gradual transition from parallel computing is identified in CompactPCI PlusIO.

Since 1995, has been implemented in countless applications, utilizing common PC chips (and proven standard software), modular Eurocard form factors (IEEE 1101.1) with high-performance connectors, and passive backplanes. However, despite withstanding almost two decades of embedded computing advancements, the CPCI bus has begun to reach its bandwidth limitations.

In response, the governing trade association PICMG developed a new specification for faster data transfer rates. Defining the new spec was certainly not a simple task. On the one hand, proven advantages of the predecessor needed to be preserved to enable users to economically benefit from their “old” system solutions. On the other hand, the requirements for future systems demanded a dramatic increase in speed. A solution could only be implemented with serial architecture – a modified architecture and communication structure- – and new high-speed connectors with higher pin density.

The result, PICMG CPCI-S.0 (or ), is impressive. CompactPCI Serial technology opens up a completely new era, supporting data transfer rates of up to 12 Gbps that offer the high-precision ideal for automated workflows. Furthermore, it provides new ways for designers to work effectively in applications that have either traditionally used CompactPCI or that benefit from the proven technology platform now enhanced with serial point-to-point connections.

High-speed connectors for fast performance

The most important factor behind CompactPCI Serial's incredible performance is its high-speed connectors. The serial point-to-point connectors replace the old parallel bus technology and are equipped with 184 signal pairs and a 3U backplane, facilitating transmission rates of up to 12 Gbps (Figure 1). The connectors are attached on four sides making them very robust, with the 'female' end of the connector attached to the backplane to reduce the risk of malfunctions. They are easy to use, even in demanding working environments, and the rear I/O utilizes the same connectors.

Figure 1: Views of the new CompactPCI Serial backplanes and their high-speed serial connectors.

The overhaul is “Serial”

In addition to the robust connectors, CompactPCI Serial has taken other important configuration aspects into consideration. The tried-and-tested PICMG 2.0 CompactPCI specification was expanded to include the USB 2.0, USB 3.0, SATA, PCI Express, and Ethernet protocols, providing the optimal environment for symmetrical multiprocessing and system redundancy. While full details can be found at, here are some of the specific attributes of the high-speed interfaces, as well as the back-end architecture[1]:

·    Up to 8 PCI Express (6 x4 lanes, 2 x8 lanes)

·    8 SATA/SAS

·    8 USB 2.0/3.0

·    8 Ethernet interfaces plus signals for general system management (reset, IPMB, hot plug, geographical addressing, among others)

·    12 V (60 W per 3U slot, 120 W per 6U slot)

Each peripheral slot, all of which are simultaneously accessible, offers one PCI Express link, one SATA/SAS, and one USB 2.0/3.0 interface. The star topology is equal for all of these, and the slots are identical with the exception of the two PCI Express x8 lanes. Congruency of the system and peripheral slot pin assignment makes plugging a system slot board into each peripheral slot possible, thus supporting symmetrical multiprocessing.

Up to eight Ethernet interfaces with transmission capabilities as high as 10GBASE-T are also supported by each slot, building a full mesh and affording the ability to configure redundant, safety-critical systems.

Extended possibilities in traditional applications

CompactPCI has always been perfectly suited for use in the areas of industry and transportation. That has not changed, but with the inception of CompactPCI Serial, the ecosystem offers additional potential in the areas of security, communication, and building technology.

Between increased computing power and integration of the previously mentioned interface protocols, projects seen as insurmountable can now be resolved. One example is in production lines that can – at anytime and from anywhere in the world – be controlled via remote maintenance. Diagnostic sensors provide system-related data and show warning signals even before reaching critical levels, enabling proactive service and prevention of system failure.

Beyond this, access to WLAN can be attained via the USB hub, and powerful, rapid storage and RAID applications can be implemented through existing SATA interfaces. This technology can be effectively employed in safety, broadband communication, and facility automation environments, and in transportation applications, passengers can benefit from greater comfort upgrades such as onboard infotainment systems and better quality climate control.

Why change to CompactPCI Serial, and how?

It may seem that the price to pay for higher speed is the loss of complete compatibility with the legacy CompactPCI platform. Particularly when designing new applications that utilize high-speed interconnects, sacrificing backward compatibility would appear a necessary evil. However, it’s against the long tradition of a system based on a standard: access to a huge software and hardware library out of which modular systems can be configured, and development of only what is required for a specific project.

One solution allowing both improved signaling and compatibility with CompactPCI comes in the form of CompactPCI PlusIO (Editor’s Note: See MEN Mikro‘s article for more information on CompactPCI PlusIO), a hybrid system that connects conventional CompactPCI computers (PICMG 2.0) to CompactPCI Serial technology. Legacy systems can remain in operation while being extended via connection to the newer serial bus through a single star topology backplane with rear I/O support.

The future is Serial

The trend is clear: future CompactPCI applications within the “traditional areas” of industrial automation and transport will demand high system speed and universal interfaces. With the new CompactPCI Serial, PICMG CPCI-S.0, a designer can develop systems capable of data transfer rates of 12 Gbps.

Profound know-how for complete or incremental transition is offered by experienced system integrators, such as ELMA. From the planning and design of the backplane and chassis up to fully integrated computers, an embedded integrator can offer a platform solution from a single source. This safely eliminates every possible source of error in transition and initial startup.

The growth of the CompactPCI ecosystem was made possible through significant modifications to the technical architecture and the change from parallel to serial bus technology. So begins the next chapter in CompactPCI computing.

Frank Weiser is Senior Design Engineer for backplanes with the GmbH in Pforzheim.

Elma Electronic GmbH

[1] CompactPCI Serial (PICMG CPCI-S.0) Specification.

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