Since its introduction in 1992, PC/104 has been one of the most popular embedded-system architectures, because of its size, rugged construction, and PC compatibility, and due to the huge array of off-the-shelf components available to developers. Often embedded in medical instruments, avionics, vending machines, test equipment, communications devices, vehicular systems, data logging, and industrial-control systems, PC/104 products take advantage of the low-cost silicon, software, and development tools from the desktop world. Like all other long-term board standards, PC/104 has undergone several revisions to keep up with changes in technology. The latest additions, EPIC (Embedded Platform for Industrial Computing) and EPIC Express offer PC/104 designers a more f lexible form factor and future access to high-bandwidth serial interconnections.
The developers of the PC/104 architecture based it on the ISA (Industry Standard Bus) from the IBM PC. The developers derived the name from the PC and the number of interface pins on the 16-bit ISA bus. Although the ISA bus is now essentially obsolete on the desktop, it still has advantages for embedded systems. Peripheral cards are simple, low-cost, and easy-to-design—all prime requirements of embedded products. The relatively low speed of the ISA bus also simplifies noise and EMI-protection schemes. Yet, the main reason for its continued popularity is the large number of off-the-shelf products from which designers may choose. Currently, there are dozens of manufacturers actively producing hundreds of unique PC/104 products.
PC/104 cards have stackthrough connectors that eliminate the need for a motherboard, backplane, or card cage. These pin and-socket bus connectors provide a reliable signal path even in harsh environments. Although the stackthrough connectors are among the positive features of PC/104, they also cause problems. Along with manufacturing headaches that connectors on both sides of the board cause, the densely packed PC/104 configuration makes it difficult to change boards, especially in the center of a stack. The PC/104 Consortium published a formal specification in 1992 that it maintains on its Web site.
COTS stackables Standard PC/104 modules come in a variety of simple and sophisticated configurations. For example, for mobile telematics, fleet management, distributed communication systems, and remote data-logging applications, the Com17035er from RTD Embedded Technologies combines a wireless dual-band modem unit and a low-power parallel-tracking GPS (global-positioning-system) receiver on a single PC/104 module (Figure 1). This module provides a direct connection to stationary or mobile GSM (Global System for Mobile communication) fields using the Siemens MC35 cellular engine in the 900-, 1800-, or 1900MHz band. You can connect any standard GSM or GPS antenna directly to the Com17035er using onboard connectors. Key features include a maximum 50kbps data rate, an onboard SIM-card socket, a headset interface, UART interfaces to a host computer, and a -20 to +70°C operating-temperature range. The module is compatible with all x86 operating systems, including DOS, Windows, Linux, and real-time operating systems, such as QNX, VxWorks, and Windows CE. Prices for the Com17035er module with adapter cable and antenna start at $695.
Since PC/104's introduction, designers have incorporated into it several enhancements to extend performance. The PCI bus has effectively replaced ISA on the desktop, and it was only natural for system architects to add it to PC/104. The PCI bus brings a much higher data rate for high performance peripherals and application-specific hardware. The PC/104 Consortium in 1997 released the specification for the PCI extension, PC/104-Plus. It gives board designers the choice of incorporating the ISA bus alone, the PCI and ISA buses together, or the PCI bus alone. PC/104-Plus requires a new connector to house the PCI-bus pins, a loss of board space that is one of the few disadvantages of the PCI upgrade.
PC/104 got another boost in efficiency in 1997, when Ampro Computers and Motorola jointly developed the specification for the larger EBX (Embedded Board Expandable)-form-factor computer board. EBX boards measure 5.75 8-in. and are large enough to implement a full 32-bit system with CPU, memory, display interface, and basic I/O on a single board. EBX also has an integral PC/104- Plus expansion interface, so users can stack off-the-shelf peripherals boards to complete a system. The EBX specification does little more than state the board's mechanical dimensions, leaving the designer free to implement almost any computer configuration.
Enter EPIC To address the board-space problem and retain a more compact configuration, Micro/sys, Octagon Systems, VersaLogic, WinSystems, and Ampro Computers joined forces to create EPIC—a new, midsized, open-architecture, embedded platform. This board is large enough for the latest CPU silicon along with basic I/O, and it maintains compatibility with PC/104 and PC/104-Plus expansion modules. The new EPIC module has a 4.5 6.5-in. footprint, a little more than twice the area of a standard PC/104 board. The EPIC specification, also available from the PC/104 Consortium, defines five board zones to accommodate large heat sinks and variable-height I/O connectors (Figure 2). Although the specification does not address functions or connectors, these zones preserve component height limitations, connector spacing, and mounting-hole locations.
With potential application in medical devices, security equipment, industrial machinery, aerospace projects, and transportation systems, VersaLogic’s latest EPIC-format single-board computer, the Gecko, operates at -40 to +85°C (Figure 3). The company bases the Gecko on the AMD GX-500 processor, which offers 500MHz-equivalent performance and draws only about 1.5W. The low power consumption results in minimal heat dissipation, eliminating the need for an onboard fan. The module’s features include maximum 512Mbyte DDR RAM, integrated video with analog and LVDS (low-voltage-differentialsignaling) flat-panel outputs, stereoline in/out, 10/100 Ethernet, analog and digital I/O, four USB ports, four communication ports, LPT (lineprinter- terminal) and IDE interfaces, and a CompactFlash socket. The PC/104-Plus site accommodates both PC/104 and PC/104-Plus modules for system expansion. The Gecko includes safety features such as transient voltage-suppression devices for electrostatic-discharge protection, self-resetting fuses for user I/O, and a watchdog timer for hardware level application control. Prices start at $673 (OEM quantities).
Targeting machine-to-machine applications, such as robotics, pipelines, medical, transportation, test equipment, security, machine control, HVAC systems that require a processor, a wide variety of I/O, and network connectivity, WinSystems recently introduced the EPX-GX (Figure 4). With 11 onboard I/O functions plus more I/O-expansion options through PC/104 modules, the EPIC-based module features the AMD GX500 processor, a Pentium-class CPU with an x86-native instruction set, and 32kbytes of integrated L1 cache that runs Windows CE, WindowsXP embedded, Linux, VxWorks, and QNX. Onboard I/O support includes 10/100 Ethernet, an 802.11 miniPCI connector, two USB ports, four communication ports, 24 parallel digital-I/O lines, 4 AGP video with a CRT and digital flatpanel interface, a keyboard controller, PS/2 mouse support, an LPT port, and AC’97 audio. The low-power design allows the EPXGX to operate over the industrial temperature range of -40 to +85°C without a fan. The EPX-GX draws typically 1.8A at 5V during normal operation. Delivery is stock to three weeks, and the price is $499 (OEM).
For expanded I/O applications, the new Micro/sys Opto104 accommodates eight industry standard digital or analog Opto plug-in modules plus any PC/104 CPU or I/O cards you need to make a rugged, compact industrial controller. You can plug any combination of digital- or analog-I/O modules into this EPIC-sized board, which targets rugged environments and extended temperature ranges of -40 to +85°C (Figure 5). Additional system-level features of the Opto104 include a watchdog timer; a rotary-encoder input; an onboard temperature sensor; and interfaces for a character-based LCD, keypad, and CAN (controller-area-network) bus. When applications demand additional I/O, you can connect as many as four Opto104 boards together in a slave configuration using a 26-wire ribbon cable. Opto104 modules provide optical isolation to as much as 4000V. The board operates at 5V or with a selection of dc/dc-converter options that allows an input-voltage range of 9 to 75V. The Opto104 costs $375 in single quantities.
Bring on bandwidth Even with an expanded footprint, the data rates of many newer applications exceed the limitations of shared-bus systems. In these high-speed applications, which handle imaging or other signal-processing problems, designers have adopted serial switched-fabric communications techniques to transfer data directly between subsystems. Because of its compatibility with driver and operating software, PCI Express has become the fabric of choice for PC compatible systems. The technology’s LVDS provides maximum bandwidth between nodes. The basic PCI Express link comprises two signal paths that use small differential-voltage swings and constant current-line drivers to communicate at a minimum of 2.5 Gbps in each direction. Low-voltage swings deliver low-noise signals at low power consumption. Designers can increase the bandwidth of an individual PCI Express link by simply adding signal pairs, or lanes, until they reach the desired performance level. The PCI Express specification supports one, two, four, eight, 16, and 32 lanes.
The EPIC Express standard extends PCI Express fabric technology to industrial embedded computers. Using the same board size as the standard EPIC platform, the Express version replaces the parallel-PCI-bus connectors with smaller, serial connectors that retain the stacking features of PC/104 architecture. The ISA connectors remain part of the specification to ensure compatibility with the thousands of legacy expansion modules. The new standard also defines a PC/104- sized EPIC Express module that you can stack with legacy modules. Unlike PC/104, the stacking order for EPIC expansion modules is significant. EPIC Express expansion modules must be closest to the base single-board computer with standard PC/104 modules on top. EPIC and EPIC Express are open hardware standards allowing designers to develop conforming boards without licensing fees or royalties. Complete implementation details and the EPIC Express specification are available for downloading from the EPIC Express Web site.
Although single-board computers and expansion modules based on EPIC Express are not yet available, the new standard promises to re-energize PC/104 design possibilities. Small-system designers will be able to combine the latest high-performance devices with off-the-shelf modules to simplify and shorten the embedded development cycle. With the relentless flow of new technology and regulations (see box “Coming down the pike”), a standard that integrates new capabilities into a popular embedded architecture deserves careful consideration.
Author information You can reach Technical Editor Warren Webb at 1-858-513-3713 and wwebb@edn.com
Coming down the pike
The ROHS (reduction-of hazardous-substances) initiatives, cell-computing technology, and the multitude of fabric options were the hot topics at the January 2006 Bus&Board Conference in Long Beach, CA, sponsored by members of VITA (VMEbus International Trade Association). Although ROHS may have its biggest impact on manufacturing companies and fabrics are still battling for first place, cell computing may significantly impact the future of board design.
Eran Strod, director of product marketing at Mercury Computer Systems, summarized the cell architecture, which Sony, IBM, and Toshiba developed: “The cell broadband engine processor is the most significant architectural advance in high performance embedded computing since vendors introduced AltiVecenabled processors more than a decade ago. Originally driven by the needs of the entertainment and gaming industries, the cell processor is the result of collaboration among the companies.
“The architecture of the cell processor features nine microprocessors on one chip: eight SPEs [synergistic processor elements] and a power architecture-compliant core, the PPE [powerprocessor element], which orchestrates their activities [Figure A]. The EIB [element-interconnect bus] provides the internal communication among the processors, moving 96 bytes/cycle. A DRAM controller provides memory access as fast as 24Gbytes/sec. This new architecture is essentially a multicomputer on a chip.
“The processor delivers 200 Gflops for 32-bit floating-point operations, an order of magnitude beyond any previous microprocessor. When mapping real applications onto the cell processor, Mercury Computer Systems achieved performance improvements of five to 100 times that of currently available processors and estimated performance-per-watt improvements ranging from three to 10 times that of other available solutions.”
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