SMALL FORM FACTOR BOARDS
Standard COM Carrier Boards Offer Benefits Over Traditional SBCs
Computer-on-Module technologies hold promise for powerful and small embedded systems. Adding the concept of standard carrier boards for application-specific I/O can greatly reduce cabling, thermal and time-to-market bottlenecks.
JONATHAN MILLER AND DAVID FASTENAU, DIAMOND SYSTEMS
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Embedded systems designers are under pressure to reduce the cost and size of electronics while improving time-to-market and overall system reliability. Today, many systems use off-the-shelf x86 single board computers (SBCs) with I/O modules stacked above or below to implement the special-purpose I/O that makes the hardware fit the application requirements. Designers understand the benefits of using a proven off-the-shelf processor board while focusing their design efforts on the application-specific and frequently custom I/O that makes their application different from others.
Traditional SBC-based systems were built using EBX or EPIC form factor SBCs or PC/104 CPUs. These boards provide expansion buses (PCI and ISA) to enable the inclusion of off-the-shelf I/O expansion modules from a broad ecosystem of PC/104 I/O modules that has grown over time to hundreds of modules from dozens of suppliers to meet diverse system level requirements (Figure 1).
Yet standard SBC-based systems with large I/O requirements have a number of significant drawbacks that have vexed embedded designers, including:
• Relatively large sizes due to the number of add-on I/O boards
• Packaging difficulties resulting from the somewhat odd format of a stack of boards with I/O connectors on all sides
• The cabling nightmare driven by the need for transition cables between the SBC and I/O modules’ pin headers to appropriate connectors on the enclosure bulkhead
• The incredible assembly and maintenance difficulties associated with a tightly integrated stack of boardsIncreased purchasing efforts and planning complexity resulting from dealing with a large number of suppliers
• Increased system cost due to the presence of expensive interconnects between boards
In response to these drawbacks of SBC and PC/104-based system architectures, the embedded board industry introduced Computer-on-Module (COM) products, which shrank the CPU to a minimum footprint and brought all I/O through a small set of standardized connectors to application-specific COM carrier boards (also known as baseboards). The form factor of each baseboard may be customized to meet the needs of the application enclosure, frequently eliminating all transition cables. Application-specific I/O functionality can be implemented on the baseboard, eliminating multi-board stacks and enabling the I/O to meet the exact needs of the application.
The attractiveness of a COM-based solution is demonstrated by the fact that COM CPUs far outsell (in unit volume) all standard small form factor SBCs, including PC/104 CPUs, combined. However, COM products bring two significant new requirements to the embedded designer. They require the design of a custom I/O baseboard for the application, which brings with it the requirement to attain expertise in the needed I/O circuitry
Until now, these requirements have limited COM solutions to high-volume applications for OEMs with board design expertise or the willingness to pay high-NRE board development fees to third parties. Frequently, time-to-market is extended while the custom board is designed and put into production and all the technical hurdles are overcome. OEMs who lack the confidence or skill to design their own baseboard or the NRE budget to pay others to implement a custom baseboard, as well as most small and medium volume OEMs who simply cannot tolerate the development cost either way, have elected to stay with an SBC or PC/104-based solution due to the lack of suitable alternatives.
Now, for the first time, a middle ground has been created in the form of off-the-shelf I/O-rich COM carrier boards in standard SBC form factors, giving designers the best of the SBC and COM worlds without the budget and schedule risk associated with a full custom baseboard solution. Even better, these off-the-shelf baseboards can be customized if needed to particular application requirements (form factor, type and location of connectors, specific I/O functionality) for far less cost and with much less risk than starting a custom I/O baseboard from scratch.
Best of Both Worlds
This new design paradigm enables traditional users of stackable single board computers (SBCs) to gain many of the benefits of a COM-based solution without having to deal with most of the drawbacks. It consists of an off-the-shelf application-oriented I/O-intensive computer-on-module carrier board mated with an industry-standard off-the-shelf COM CPU. Using this approach, a two-board “sandwich” (COM CPU plus carrier) provides a complete application solution that may have previously required three, four, five or more stackable I/O modules in addition to a CPU card.
By using off-the-shelf industry standard COM modules as the CPU, each of these new carrier boards can support a wide performance range of solutions–effectively an instant product line. The new approach offers significant advantages over traditional stacked solutions in addition to greatly reducing overall system size. The approach enables a more reliable, easier to assemble solution with reduced and simplified cabling. In addition, widely popular COM CPUs are frequently much less costly than an equivalent CPU on a larger single board computer form factor.
An example of the new direction is Diamond Systems’ Neptune SBC, implementing a rugged, extended temperature, I/O-rich high-integration ETX baseboard (Figure 2). The baseboard integrates the capabilities of five traditional PC/104 I/O modules into a single EPIC-sized board. Unlike ATX-style reference design carrier boards offered by COM suppliers, this baseboard is intended as a standard product for production deployment. However, as OEM production volumes grow, or if a different set of I/O is required, the baseboard design can be modified as needed.
The use of the industry standard ETX interface offers a wide performance range of available ETX CPU modules. The ETX CPU plugs into the bottom of the baseboard, which allows the implementation of an efficient thermal solution by conducting the heat from the processor and chipset directly to the bottom surface of the enclosure.
With an ETX module attached (Figure 3), the standard baseboard concept includes an extensive set of standard PC I/O such as four USB 2.0 ports, Serial ATA (S-ATA) and EIDE hard drive interfaces including CompactFlash socket and IDE Flashdisk interface, 10/100 and Gigabit Ethernet controllers, six RS-232 serial ports (four with RS-422/485 capability), AC’97 audio, and legacy keyboard and mouse interfaces. While providing all this I/O, Neptune includes a PC/104-Plus expansion (PCI and ISA buses) interface to accommodate still more I/O if needed.
This extensive collection of I/O features is organized conveniently as a row of pin headers along the front edge of the board. To eliminate transition cables altogether, an optional Panel I/O Board plugs directly into the front edge pin header row.
Neptune also optionally offers advanced, comprehensive, integrated data acquisition capability, with 32 single-ended (16 differential) analog inputs with 16-bit autocalibration A/D, 250 KHz sample rate and 1024 sample buffer, four analog outputs with 12-bit D/A and 100 KHz waveform output capability, 24 programmable digital I/O lines, 8 optically isolated digital inputs, 8 optically isolated digital outputs, and two counter/timers. The analog I/O circuitry supports interrupt A/D transfers and uses an enhanced FIFO with programmable threshold for maximum flexibility and data reliability.
Unlike the typical ATX-style carrier boards that are large and require multiple input voltages, the embedded carrier board requires only a single input voltage. A wide input voltage range of 5-28V DC is supported on the board, without requiring an external power supply, making it suitable for many industrial and vehicular applications. Neptune packs all of the I/O and power circuitry into a tiny 4.5 x 6.5” (115 mm x 165 mm) board, in compliance with the EPIC 2.0 specification.
The standard carrier board concept makes possible a family of single board computers, supporting different ETX CPU options installed on the bottom side, initially Neptune-LX with an AMD LX800 processor and Neptune-PM with a 1.4 GHz Pentium M 738 CPU. OEMs selecting a standard baseboard solution gain the benefit of COM CPU without the need to deal with the potential customization issues involved in the inclusion of other ETX CPU choices.
For OEMs for whom the baseboard does not provide the specific I/O functionality required or who require a different form factor and/or connector implementation, Diamond Systems has announced their ETX-Based Application-Specific Program to customize the Neptune baseboard to a specific set of requirements. Due to the proven functional blocks of the design and components selected for long-term availability, customization of a COM baseboard is much less costly and time-consuming with much lower risk than starting a new baseboard design from scratch. Figure 4 represents how custom I/O blocks are attached to buses from the ETX module.
Over the next several years, Diamond Systems will bring additional, application-specific ETX baseboards to market that will serve both as off-the-shelf solutions and as the starting point for a quick and easy customization to meet additional specific application needs. The goal is to deliver faster time-to-market with more efficient solutions, lower risk and lower cost.
Many more embedded system manufacturers of all sizes can now move to the latest Computer-on-Module technologies and architectures without incurring the schedule, risk and cost of custom baseboard development.
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