industry outlook Consortia crossfire An advanced course on PC/104 Editor’s note: As chairman of the Q & A with Jim Blazer, PC/104 Embedded PC/104 Embedded Consortium’s Technical Committee and CTO for Consortium Technical Committee RTD Embedded Technologies, Jim Blazer is accustomed to fielding PC/104-related inquiries. He took some time to answer our burning questions as well as share common questions and answers he has been compiling for a PC/104 FAQ that will soon be posted at the consortium’s website, www.pc104.org. BLAZER: When the opportunity to do Embedded processors evolve from laptop power may not be a limitation in future a Q & A for PC/104 and Small Form processors, not desktop processors. In a processors. Factors arose, I was intrigued. Admit- laptop, size and weight are high-priority tedly, I was expecting the typical “What considerations, and such a large heat sink One final note: Assigning a maximum is PC/104?”, “How many cards can be in is not practical. If you open a similar processor power number to a PC/104 a system?”, and similar queries. While modern laptop, you will see a much more system is akin to saying “no one will these questions are important, they have refined cooling system. Small, sleek, need more than 640 KB of memory.” The already been addressed in numerous and sophisticated. Also, the laptop takes simple answer is that the combination of articles and specifications. Consequently, advantage of power-saving options in the low-power/high-performance processors I was relieved when I saw the list of ques- processor, such as slowing down when not and advanced heat-sink technology will tions for this interview and realized that being used or when the temperature gets allow PC/104 manufacturers to use the we were doing something a bit different too high. The same features that make a latest-generation processors. – something much more informative and good laptop processor are also the features interesting. I hope you agree. required for embedded processors. EDITOR: PC/104 is ISA based, and ISA is disappearing from x86 EDITOR: We have been noticing lots Embedded designers can take advantage chipsets. How is this being dealt with? of Pentium M-based PC/104 boards in of these processor power-saving options. Are PC/104-only solutions obsolete the market today. What’s the thermal They also have control over the enclosure, compared to PC/104-Plus and limitation for a processor selected? which can have a significant impact on PCI-104? Provide a technical the power rating. If an application does perspective, not a market share. BLAZER: Instead of trying to determine a not have a height limitation, a larger heat PC/104 board’s absolute maximum power sink or fan can be used. This will require BLAZER: I think I first heard that ISA rating, which depends on many factors, the CPU to be the top board in a stack; was dying in 1985. I suppose that rumor let’s consider the real issue: Will PC/104 however, other novel cooling options are seemed accurate, but here it is, 2007, and continue to support the latest-generation being built into many enclosures. Many of people are still asking this question. processors? The quick answer is yes, but the same advances in heat-sink technol- let me explain. ogy being used in laptops can be applied ISA has been around for a long time. It to PC/104 systems. Metal heat sinks, heat has proven to be a rugged, reliable bus If you’ve opened your desktop PC in the pipes, and active coolers will facilitate the for embedded systems, and PC/104 has last few years, you probably noticed that use of higher-power processors. boosted its popularity. For these reasons, the processor no longer has a simple pas- I am reluctant to predict its demise. sive heat sink. In fact, it looks more like That being said, all the major processor a skyscraper of fins, multicolored metals, manufacturers are building lower-power, The PC/104-Plus and PCI-104 specifica- and fans. These computers are designed higher-performance processors. As the tions were developed to provide a future to operate at 25 °C. How can these pro- die geometries get smaller, the power for PC/104 systems. Much as PCI has cessors work in PC/104 applications gets lower and the performance increases. replaced ISA in desktop computers, PCI that must meet full commercial and even Manufacturers are building more power- is slowly gaining on ISA in PC/104 sys- industrial temperature ranges? saving options into newer processors, so tems. But the embedded market moves slowly, and PC/104 is keeping ISA alive. Pentium M processors are being built with PC/104’s ISA bus. PCI-to-ISA bridges and cores will help keep ISA going. There is a way to keep ISA alive, and its name is PC/104. EDITOR: What types of power supply Figure 1 solutions are available for PC/104? Are there stackable power supplies? Likewise, many other form factor CPU Another enclosure option is a modular BLAZER: Yes, there are stackable power boards offer a PC/104 expansion port approach in which every board is in a supplies as shown in Figure 1. The stack to support upgrades. Maybe you need frame, with the I/O for that board brought options include PC/104, PC/104-Plus, and to add faster Ethernet, a field bus inter- out to the frame as shown in Figure 4. PCI-104 power supplies in many power face, or a new data acquisition board. This approach maintains PC/104’s mod- ratings. ATX power control, isolation, You can find PC/104, PC/104-Plus, and ularity, as the frames can be stacked and uninterruptible with battery backup PCI-104 slots on desktop/industrial ISA following PC/104 rules for modules. are some of the options, as are tempera- and PCI boards, Mini-ITX, EBX, EPIC, Add a top and bottom, and you’ve got a ture range and input power source. CompactPCI, VME, Eurocard, and other complete system. form factors. Figure 2 shows a PC/104- An external supply can be a small power Plus board on an EPIC baseboard. Custom enclosures can offer military con- brick that provides +5 V to a CPU or nectors, waterproof designs, multicolor, small stack or the supply in a larger and a wide variety of mounting options. system hosting the PC/104 system. Many Some examples are depicted in Figure 5. PC/104 systems are powered through the bus from a larger motherboard. Browse through the products section of the PC/104 Consortium website to find Generally, powering a PC/104 stack enclosure vendors. through the bus provides a much better solution than powering from an external EDITOR: Some oversized PC/104 +5 V supply wired directly to a power boards are being introduced with connector. Modern processors can change Figure 2 “wings” for extra real estate. What are their current demands very quickly. Wire the considerations in using one of those? inductance and resistance can cause a great deal of voltage noise from the A typical PC/104 system will have a BLAZER: The PC/104 specification changes in current demands and can initi- stack of boards with their I/O wired to defines a 3.6" x 3.8" board with connec- ate system resets if done incorrectly. a common connector panel. The whole tor areas that extend 0.5" from the edge stack then slides into some type of tube. of the board. The PC/104 specification For a list of power supply vendors, visit the Figure 3 provides an example of this states “I/O connectors may overhang in PC/104 Consortium website’s products configuration. this area (includes mating connector).” section at www.pc104.org. EDITOR: What types of chassis are available for PC/104 systems? BLAZER: The first option is no enclo- sure. Many PC/104 stacks are simply mounted inside an existing enclosure by the four mounting holes. PC/104 boards’ small size allows them to be used stand- alone or in a mezzanine application. As a system component, CPUs can be placed on an I/O board, freeing engineers to use a CPU from the wide selection of PC-compatible PC/104, PC/104-Plus, or PCI-104 CPUs on the market. Figure 3 industry outlook System and enclosure designers must allow boards to have I/O connectors in this area. While wings may not meet the letter of the specification, if they do not extend beyond the connector area, including the mating connector, they meet the spirit of the specification. If you are using a board with wings, you must be sure that the enclosure you select has room for not only the wings, but also any wiring that must go between the wings and wall. EDITOR: Should the pads for the Figure 4 PC/104 mounting holes be grounded? BLAZER: The PC/104 specifications do not say anything about grounding the mounting holes. Some PC/104 manu- facturers ground them, others leave them unconnected, and still others provide an option to ground them. Deciding whether or not to ground mounting holes and cases is a system design issue. You must have a good ground with no loops to ensure the best performance, but some applications may require complete isolation. In practice, if a board has the mounting holes grounded, nylon spacers can be used to isolate them. If the mounting holes on a board are not grounded, a metal spacer will carry ground through to the other cards in Figure 5 the system.