Don't mistake small for delicate: Bringing rugged computing to compact environments

3ESMexpress and the even smaller ESMini combine ruggedization with the cost-savings of COMs to open the door for designers to employ these compact embedded computers into a wider variety of mobile, industrial, and rugged applications.

The original Computer-On-Module (COM) concept from the early 2000s was an important step in small form factor computing. The modular COM concept sought to enable the expansion and customization of an embedded system through application-specific carrier boards. Configuring the I/O on an individual carrier board according to an established industry standard allows the system designer to tailor the functionality to the application, save development costs, and shorten time-to-market.

Since the pure CPU functions can easily be standardized for many fields of use, the COM-based system can use a more or less standard plug-in CPU module. Only the carrier board needs to be designed or adapted to the application, making this a less complex and less expensive proposition, and special I/O interfaces, memory devices, connectors, or form factors may be added to the carrier board for increased flexibility. Also, FPGA-based functions can be added to a carrier board or to the CPU module, if desired.

One limitation to the COM concept was its inability to withstand rugged, shock- and vibration-laden environments. The reasons were two-fold. First, the connector was not sturdy enough to avoid damage during more rigorous handling, such as moving from location to location or during higher levels of vibration. Second, the module components themselves were unable to withstand this handling and vibration as well, since they were not fastened to the board in such a way that would allow them to remain unharmed.

This precluded the use of this highly cost-effective and modular concept in a number of harsh, mobile, and mission-critical embedded applications such as airplane, ship, and train control; mobile test systems; mobile medical equipment; and industrial control systems.

Today, the proposed ANSI/VITA 59 RSE (Rugged System-On-Module Express) standard, currently in development with VITA, capitalizes on the small form factor and interchangeable concepts behind the original COM.0 standard. Yet ESMexpress, as it is also known, and its smaller cousin ESMini, take COMs to new levels of performance by including rugged performance characteristics, such as operating temperatures ranging from -40 °C to +85 °C, shock resistance up to 15 g/11 ms, and greater immunity from EMC emissions, while offering a broad range of end-user choices for microprocessor architecture including Intel and PowerPC options, I/O versatility, and programming flexibility via changeable and upgradable modules.

Reengineered for ruggedization

ESMexpress is based on COM Express, and therefore the two share some important similarities. Both utilize the same compact 125 mm x 95 mm board size, implement CPU functionality on a standardized module, and enable the carrier card to handle unique application requirements including I/O interfaces, extra memory devices, and connectors. But there are distinct differences as well (Table 1, page 18).

Table 1: Although built on the COMs concept, ESMexpress has distinct differences that make it reliable in mobile, rugged environments.
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The rugged aspects of ESMexpress make it resistant against temperature, shock, vibration, and EMC influences, and enable these boards to function reliably in life-critical applications or applications that entail high costs in case of failure. These include applications in ground transport or airborne equipment, practically any mobile computing environment, avionics or medical engineering, as well as outdoor computers and critical industrial control equipment.

Tough traits

The electronics are completely housed in an aluminum enclosure that provides optimum EMC protection. The module is mounted on the carrier board, so all six sides are hermetically sealed, and conforms to EN 55022 for radio disturbance, to EN 55024 and EN 61000-4-2 for electrostatic discharge (ESD), and to EN 55024 and EN 61000-4-4 for burst (Figure 1). Maintained by the European Union, these standards offer limits and methods of measurement to ensure the reliability and durability of electronics within systems over extended periods of time. Radiated and conducted emissions are regulated by EN 55022 and immunity is monitored by EN 55024. EN 61000-4-2 determines electronics’ immunity to ESD and EN 61000-4-4 defines the immunity of electronics to switching and transient noise inherent in the system. Both of these standards meet class B limits where, after the equipment has been tested, it will continue to operate as intended without user intervention.

Figure 1: The configuration withstands extreme shock and vibration via the aluminum housing, which also provides exceptional EMC protection.
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The connector is especially rugged in part through its qualification for railway applications. It is specified for -55 °C to +125 °C and supports differential signals up to 8 GHz.

Optional conformal coating provides added protection for harsh operating environments where dust or moisture are concerns. Fully soldered connections provide shock-resistant and vibration-resistant performance rated to withstand 15 g/11 ms for shock and 1 g/10 Hz to 150 Hz for vibration (sinusoidal).

Keeping cool

One of the more unique, and most important, aspects is the fanless cooling concept, designed to dissipate up to 35 W. For compact environments that are densely packed with a multitude of high-functioning components, this proves critical to system reliability to avoid failure due to heat build up.

The metal frame, metal cover, and mechanical connections of the ESMexpress assembly 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 thermographic imaging demonstrates just how much of a cooling effect adding the frame to the PCB exerts on the design (Figure 2).

Without the conductive frame, the hottest spot on the module reaches a temperature of more than 87 °C, yet is under 81 °C when the cover is secured. Similarly, the processor core, as well as several other components, drops an average of 4 °C once the cover is screwed into place.

Figure 2: The PCB/frame connection dissipates significantly more heat generated by the processor using the conductive frame (left) versus a unit with no cover (right).
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If additional cooling is needed, an external heat transfer device (conduction) can be added or the board can be combined with a heat sink for heat dissipation (convection). Conversely, the dissipated heat can also be led from the cover via the frame to a carrier board that supports conduction cooling.

Versatile communications

Modern serial buses, without switched fabrics, are compatible with a variety of standard operating systems. The extensive range of communications protocols – including PCI Express, Gigabit Ethernet, USB, SATA, SDVO, LVDS, and HD audio – supported by the ESMexpress standards, chipsets, and available carrier boards empower a wide variety of applications.

Distinct interface execution varies depending on the application, but this rugged, compact concept allows a wide range of options:

  • 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 Mbps, offering flexibility 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 MBps
  • For PCI Express, there are four single-lane ports (4 x1) and one port that can be configured as 1 x16, 1 x8, 2 x4 or 2 x1
  • Ethernet options provide up to three 1 Gb ports of 1000BASE-T (also 10 Gb)
  • Full-featured 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 with ample flexibility to configure the specific I/O requirements they want

Display port and HDMI support 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 available with the I/O reference voltage indicated by the CPU board on the J1-43 pin. Serial RapidIO is supported on all pins formerly dedicated to PCI Express.

Interoperability options

The signals on ESMexpress are led to two 120-pin connectors and exclusively defined for modern serial buses like PCI Express, Ethernet, SATA, and USB. The pin assignment is fixed without options in order to guarantee 100 percent interchangeability between the modules.

Any required legacy I/O as well as additional modularity can be realized using FPGAs on the carrier board. This design facilitates a resource-sharing concept of using available IP cores to configure the FPGAs and enhance specific functionality. With the FPGA functionality provided on the carrier board via a PCI Express link, instead of on the COM module itself, the number of pins reserved for FPGA functions are less than if the FPGA resided on the COM module.

The fixed assignment of the processor and the SDRAM functions on the CPU module eliminates the need for complex and expensive changes to that unit. Conversely, licensing IP cores to execute specific I/O requirements through carrier board FPGAs is a quicker and more affordable way to adapt to custom application inputs while keeping overall size to a minimum.

Further size reduction with ESMini

A variation also exists for designers requiring an even smaller form factor that still boasts the rugged advantages of ESMexpress and modular concepts inherent in COM Express. With dimensions of 95 mm x 55 mm, ESMini does not adhere to the size conventions of the proposed ANSI-VITA 59 RSE standard.

It does, however, include the same mounting frame and cover design for conductive cooling with comparable thermal, mechanical, and EMC performance levels as ESMexpress, as well as all the ruggedization features of its larger cousin (for example, an operating temperature range of -40 °C to +85 °C). And the format complements the modern serial connectivity of ESMexpress with the added ability to provide industrial I/O like CAN and UART interfaces implemented through FPGA capabilities.

This capability also makes the ESMini an attractive option for mobile and rugged applications where connectivity with legacy interfaces is an issue, since the module can easily and cost-effectively incorporate these older communication protocols on the FPGA.

Both the form factor and the pin assignment are variable. Thanks to this flexibility, individual I/O in the onboard FPGA can be implemented in addition to the serial I/O.

Small solutions with big options

Compact form factors are an attractive resource for space-constrained applications in fixed or mobile computing environments. Rugged design characteristics, including extended temperature operation and high resistance to shock and vibration, open up the versatility of the COM concept to a wider range of applications than ever before:

  • Signal, control, or passenger information systems in railway applications
  • Industrial robotic applications, from plastics production to semiconductor clean-room production and general automation
  • Extreme industrial environments such as highly precise, fast robots for motor vehicle production, or the control, monitoring, and function management of a nuclear power plant
  • Demanding mobile computing needs such as medical equipment or transportation applications

And the broad range of high-speed serial interfaces – from USB (480 Mbps) and SATA (100 MBps) to Ethernet (1 Gb/10 Gb) and PCI Express (250 MBps) – plus the versatility of FPGA customization provides cost-effective adaptation to a wide range of computing environment needs.

Compact embedded systems developers who appreciate the advantages of the COM concept will now be able to extend development into more rugged-environment applications. And those who have been precluded from adopting the COM concept because of their extreme rugged requirements will now be able to access the cost-efficiency and convenience of COM technology to get new designs to market quicker than ever.

Barbara Schmitz is Chief Marketing Officer of MEN Mikro Elektronik. For the past 19 years, her work has included public relations, product positioning, and development and coordination of global sales channels. Barbara graduated from the University of Erlangen-Nürnberg, studied business economics in a Bad Harzburg business school correspondence course, and completed a marketing and communications apprenticeship in Nürnberg.

MEN Mikro Elektronik GmbH (215) 542-9575