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By Dan Hebert, PE, Senior Technical Editor
The natural progression of controllers and computers is one of shrinking size, increased performance and lower costs. For embedded machine control applications, this progression is perhaps best expressed by the computer-on-module (COM) trend, and more specifically by the COM Express specification.
The COM Express spec is hosted and supported by PICMG, a consortium of companies that collaboratively develop open specifications for high-performance industrial computing applications. A COM Express module contains all of the components for a host computer attached to a single carrier board.
Some vendors claim that machine builders have embraced COM Express products for various applications. “Information from VDC Research Group and from our own experience shows significant COM Express penetration in industrial control applications for machine and robot builders,” says Christine Van De Graaf, product marketing manager for the embedded modules division at Kontron.
She says the key features that make COM Express attractive include the availability of PCI Express, serial ATA and Gigabit Ethernet interfaces. “These create the data bandwidth required for machine control systems,” observes Van De Graaf. “The availability of these advanced interfaces and the scalability of a standard modular solution have made COM Express the fitting integration path for industrial HMI and portable devices.”
Many embedded machine control applications require significant processing performance and extensive I/O functionality in a small package, and COM Express meets those needs, argues Doug Mays, technical marketing specialist with Diversified Technology. A white paper by Diversified Technology outlines how COM Express can help machine builders save time and money. The standard for a COM Express carrier board is CPU-agnostic. This keeps performance up and prices down as companies compete to offer the best processor, all in adherence to the spec.
The board-to-board connectors in COM Express consist of two rows. One row provides pins for PCI Express, LPC bus, serial ATA, LVDS LCD channel, VGA and TV-out, LAN and system and power management, as well as power and ground interfaces. The second row provides SDVO and legacy IDE and PCI signals with additional PCI Express, LAN and power and ground signals.
The physical dimension requirements of the COM Express CPU module allow for a basic size measuring 125x95 mm and an extended version at 155x110 mm. The extended form factor has a larger power budget, doubles memory capacity, uses dual-channel RAM configurations and allows the use of larger processors and chipsets. The basic and extended form factors share the same board-to-board connections, signaling definitions and mechanical assemblies so any carrier board can support a basic or an extended CPU Module.
“COM Express is a very flexible architecture due to its significant I/O capabilities, CPU-agnostic design and the ability to interchange host CPU modules,” adds Mays.
Competing standards such AdvancedTCA and MicroTCA focus on telecommunications and data applications and can’t support significant amounts of I/O. This makes these standards unsuitable for most machine control applications.
But COM Express products have high processing and I/O bandwidth in a small physical footprint. Designers of embedded systems can also partition COM Express CPU modules to create specialty I/Os and FPGAs using COM Express as a processing mezzanine. In doing so, these designers can focus on application-specific I/O on a custom baseboard without the need to address high-speed switched fabrics, signal reflections and impedance controls.
COM Express also represents a significant reduction in lifecycle costs. Once a specific carrier board has been implemented, future hardware upgrades can be implemented by simply changing the COM Express module. This significantly reduces the hardware costs of upgrading, which can represent the bulk of expense, when a new generation of CPU and RAM technology becomes available.
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