New standard takes COM to the extreme
ver since the initial introduction of the computer-on-module (COM) concept and subsequent acceptance of the PICMG COM.0 standard, embedded systems designers have reaped a variety of benefits from this modular concept. The easier replacement of one module with another of compatible form, fit, and function has enhanced design flexibility in compact packaging, extended application versatility, and reduced development time and cost.
In the past, however, similar benefits were not readily accessible for rugged systems operating in harsh environments. Through a new ANSI-VITA standard, an updated implementation of the COM technical concept (also known as system-on-module or SOM) is now expanding the benefits of COM-type designs to more demanding mobile, harsh-environment, and safety-critical applications.
The new design standardizes module size and pin connections while enabling CPU choice according to application needs. The customizable modules plug on carrier cards to provide unique I/O connections and other functionalities required for specific applications.
But the most significant innovation is that specifications for the plug-on module address attributes necessary to deliver mechanical stability, rugged physical performance, and aggressive fanless cooling for heat dissipation--even in harsh operating environments.
Raising the bar
The new ESMexpress computer-on-module design--currently in the process of being adopted as the ANSI-VITA 59 RSE (Rugged System-On-Module Express) standard--goes well beyond the physical limits of COM Express (PICMG COM.0) and its latest revision in 2005. Multiple features of the ESMexpress design enable it to function more efficiently by reducing power requirements and dissipating heat more efficiently. Instead of being limited to the -40°C to +85°C operating range of COM Express, ESMexpress can offer performance up to a range of -55°C through +125°C.
And, unlike other COM standards limited to x86 chipsets, ESMexpress is processor independent. It accommodates a variety of Intel, PowerPC, and other chipsets--provided they don't exceed a power dissipation of 35 W--to satisfy application-specific requirements ranging from low-power mobile apps to high-end communications platforms.
ESMexpress modules are built on a 95 mm x 125 mm form factor, leaving a full 85 mm x 115 mm of usable board space for electronic components, with no loss of space for mounting holes. That form factor is compatible with COM Express carrier boards (and vice versa) using an adapter board that complies with the COM.0 Basic Form Factor Type 2 and adapts connector placement and pin-out. This allows users to employ existing modules in either format, within the appropriate application environments.
But the essence of the new ESMexpress standard is in the design specifications. ESMexpress can function in more extreme application environments not supported by COM Express or the majority of the other COM concepts. The initial specification draft for ESMexpress was issued in April 2008, and refinements are currently being developed with respect to the ANSI-VITA 59 RSE standard. Here are some highlights of the current design.
Aggressive built-in cooling concepts.
The ESMexpress design includes multiple mechanical and thermal features to protect the plug-on module and provide conductive and convection cooling in fanless environments as Figure 1 shows. Although ESMexpress sets a threshold of 35 W for power dissipation, many of the specific CPUs used in current ESMexpress modules actually draw only a fraction of that power. These low-power processors improve compatibility for mobile applications and minimize cooling concerns.
Click on image to enlarge.
ESMexpress' metal frame, metal cover, and mechanical connections are important contributors to the thermal performance of the overall design. Both the PCB itself and the metal frame help to draw heat away from the processor and transfer it to the cover. The hottest components within the unit are also coupled directly to the cover. Eight mounting screws secure the entire physical assembly in place and ensure a positive connection for optimum heat transfer. Comparative thermo-graphic imaging in Figures 2A and 2B demonstrates just how much of a cooling effect adding the frame to the PCB exerts on the design.
Click on image to enlarge.
If a module requires additional cooling, the aluminum housing protecting the processor can also be connected to an external heat transfer device (conduction) or combined with a heat sink for heat dissipation (convection).
Rugged design and construction
The two mechanically robust 120-pin connectors that provide ample connections for I/O intensive applications are already qualified to military and railway applications and are compatible with ANSI 30.1 for 2-mm Eurocard connectors as well as ANSI 46 (VPX) for high-speed connectors. They support differential signals with up to 8 GHz and are specified for environments ranging from -55°C to +125°C.
In addition to its cooling function, the aluminum housing covering the PCB of the ESMexpress module also provides EMC protection conforming to EN55022. And for particularly harsh operating environments, where dust or moisture is a potential concern, conformal coating is optional for added protection. Fully soldered connections provide shock- and vibration-resistant performance rated to withstand 15g/ 11ms for shock and 1 g/10 Hz...150 Hz for vibration (sinusoidal).
Versatile communications options
Modern serial buses, without switched fabrics, provide high reliability for harsh-environment and mission-critical applications and are compatible with a variety of standard operating systems. The extensive range of communications protocols supported by the ESMexpress standards, chipsets and available carrier boards empower a wide variety of applications. Standardized pin assignments guarantee 100% interoperability between any ESMexpress module and ESMexpress carrier boards.
Distinct interface execution varies depending on the application, but the ESMexpress standard allows:
• Up to eight USB 2.0 host ports (or seven host ports and one client port, adjustable by software) provide data rates up to 480 MB/s for a wide range of end-use functions.
• Up to three Serial ATA (SATA) communications ports, available through the ESMexpress connector via a PATA-to-SATA converter, support RAID functions and provide data transfer rates up to 100 MB/s.
• For PCI Express, the four single-lane ports (4 x1) and one port can be configured as 1 x16, 1 x8, 2 x4, or 2x1.
• Ethernet options provide up to three 1-Gb ports of 1000Base-T (also 10Gb).
• SDVO and LVDS ports support graphics-oriented applications.
• High-definition audio is available via the ESMexpress connector.
• Extendable I/O, controlled through FPGAs, provides embedded system designers flexibility to configure specific I/O requirements. With the FPGA functionality provided on the carrier board via a PCI Express link, instead of on the COM module, the number of pins reserved for FPGA functions are less than if the FPGA resided on the COM module.
Display port and HDMI support recently added to the original specification allows for a second GMBUS defined on PCIe x16 split signals. A low voltage I/O mode (3.3 V or 1.5 V I/O) is now available with the I/O reference voltage indicated by the CPU board on the J1-43 pin. Serial Rapid IO is supported on all pins formerly dedicated to PCI Express.
Additional work is in process to define compliant mechanics to VITA30 to allow for the use of modules with cPCI and VPX by substituting the module frame with an integrated frame on the carrier board. ESMexpress also provides for a universal test and development carrier in an ATX format for evaluation of all functions on ESMexpress modules.
In addition to the 125 mm x 95 mm ESMexpress module currently being formalized as the ANSI-VITA 59 RSE standard, a smaller module using the same rugged design with modern serial communications is now available in a 55 mm x 95 mm size, shown in Figure 3.
Click on image to enlarge.
This more compact module, the ESMini, incorporates Intel Atom processors with up to 1.6 GHz of clock speed and less than 7 W of power consumption. Although ESMini is not specifically part of the ESMexpress standard, it follows the same specifications for rugged performance and cooling as the original ESMexpress modules.
Rugged applications that require mobility will keenly benefit from this technology in its smaller form factor. One growing area is precision farming based on the concept of intelligent farm vehicles, automated vehicles controlled via computer instead of by manual operation.
Precision farming combines advanced technologies, including GPS, sensors and aerial imagery, with data management tools to assess and understand variations in agricultural conditions. These include soil acidity, moisture, particle sizes, and mineral content in various land masses. Information collected by the vehicle on the fly in a single pass is instantly processed to help the in-field vehicles evaluate fertilization needs from field to field more precisely.
By maximizing the productivity of farm equipment and minimizing the use of chemicals, water, and fuel, farmers will save time and money while potentially increasing crop yield.
Keeping pace with real world
As embedded system applications move farther afield, demand longer life in mobile applications, and encounter increasingly difficult environmental challenges, the ESMexpress standard opens up a wealth of technological capabilities for mission-critical applications previously not addressed by COM designs.
Equally important to system designers and manufacturers is affordable, reliable implementation. Segregating more complex and critical CPU functions onto modules with standard pin assignments, regardless of their function, and allowing application-specific functions to be resolved on easily adapted carrier boards complements the best of both worlds--cost-effective functionality with timely application-specific development.
That combination of performance and economy offers new promise for real-world applications ranging from high-profile security and video surveillance as well as biometric access control to robotic and industrial control systems, mobile test, control, and infotainment systems across a variety of vehicle and transportation environments.
Barbara Schmitz is the chief marketing officer of MEN Mikro Elektronik. Her tasks include public relations and product positioning as well as development and coordination of global sales channels. Schmitz graduated from the University of Erlangen-N¼rnberg.