A COMIT™ Impacts Embedded Systems Design

By Robert A. Burckle, Vice-President, WinSystems, Inc.

A new form-factor independent, embedded processor module interface standard called COMIT was introduced at the Embedded Systems Conference in San Jose, California in April 2009. COMIT stands for Computer On Module Interconnect Technology™. It is targeted towards small form factor solutions leveraging the latest ultra-mobile and moderate power processor/chipset combinations. COMIT is an electromechanical connectorization specification that focuses on bus interconnect and module manufacturing technology rather than any individual processor architecture. Its purpose is to provide a compact, stackable, COM solution for future embedded systems designs which are suitable for industrial environments using the newest low power chip sets.

COMIT is a fresh design idea that separates form factor standards from board interconnect standards. COMIT supports both serial high-speed I/O and legacy interfaces while independent of module size or implementation. COMIT is designed to be I/O-centric and to be the enabling technology to allow tiny processor modules to fit within the footprint of industry-standard, small form factor boards such as EBX, EPIC, SUMIT-ISM™ and PC/104 or any other standard or custom-designed baseboards. This technology enables easy migration to future processors for performance/ feature enhancement and also prevents obsolescence for longer product life cycles.

One of the key enabling technologies of COMIT is the high-speed connector. It is the foundation for long-term, reliable system design. The COMIT connector system needs to support PCI Express 2.0, USB 3.0, and SATA 300 signaling rates. The SEARAY™ connector system from Samtec is better suited than all existing COM connectors for COMIT’s requirements — high speed, high pin density, ruggedness and moderate cost. It is a 240-pin high-density (0.050-inch pitch) connector pair that is second sourced by Molex. SEARAY™ is designed as an open pin field array configuration organized as six rows of 40 gold-plated pins to allow optimal routing and maximum design flexibility.

The connector system is capable of a differential signaling rate of 9 GHz bandwidth (at -3dB insertion loss) to support current and future high speed signaling for interfaces, whereas existing COM connectors can’t handle high frequencies. Real-world signal integrity testing has verified COMIT’s high speed capabilities. These extremely rugged, 240-pin connectors are among the lowest cost-per-pin and highest densities available on the market for this type of Gigahertz-capable interconnect.

The contacts in the SEARAY system are robust and allow for “zippering” when mating and unmating the connectors. This contact design lowers the insertion and extraction forces which is an important consideration with 240 pins. Each pin is rated for 2.7 Amps and the connector will operate over the temperature range of -55°C to +125°C. The rugged connector system is good for over 2000 mating cycles, is RoHS compliant, and is ideal for industrial environments.

Figure 1. COMIT uses a 6 x 40 SEARAY™ connector system

COMIT was designed to support embedded computing architectures with a mix of forward-looking bus interfaces with a few popular legacy I/O ports. COMIT connector pin assignments are optimized for signal integrity, relative baseboard layout ease, and optimal module routing with small form factor chipset and processor solutions available from Intel and other mobile processor vendors.

Figure 2: COMIT uses a 240-pin high speed connector to support a variety of signals

Since COMIT was developed under the auspices of a Small Form Factor Special Interest Group (SFF-SIG) working group, there is an independent industry standards body with broad market and vendor involvement responsible for its continued support. The SIG’s philosophy is to embrace the latest technologies, as well as maintain legacy compatibility and enable smooth transition solutions to next-generation interfaces.

What is included in the COMIT connector?

  • PCI Express – Three PCI Express x1 links plus one PCI Express x4 link optionally divided into four x1 links
  • USB – Six host ports: Can be OHCI, UHCI, EHCI, plus one can be configurable as a target/device port
  • Video – VGA, Dual Channel LVDS, and SDVO
  • SATA – Two Serial ATA mass storage interfaces
  • HD Audio – High Definition Audio CODEC interface
  • Low Pin Count (LPC) Bus – For interface to legacy devices
  • SPI, Microwire, SMBus, I2C – Simple serial buses for slow to moderate speed serial interfaces
  • Power - 3.3V, 5V, 3Vsb: up to 100W of power to the processor module

Why these interfaces?

High density connector pins come at a cost, both in terms of material costs and board space. When the SFF-SIG considered both current and future chipset offerings for small form factor modules from embedded chipset vendors, it became clear that purposeful choices needed to be made to address the needs of today and tomorrow. PCI Express, USB, SATA, HD audio and video were easy choices for COMIT. However, including older parallel buses in any new connectorization scheme chews up both valuable, high-speed capable pins and relegates this valuable space and resources for I/O interfaces that are either moving towards obsolescence or that should be included on the baseboard. Yet legacy devices such as keyboard controllers and serial ports are still a vital part of embedded systems today and are supported by the LPC, SMBus, SPI, SDIO, and I2C. In COMIT, Super I/O devices that normally contain the keyboard/mouse controller, serial ports, printer port, etc. are included on the baseboard which is physically separate from the processor module.

To address power supply issues, ample power and ground pins are designated on the COMIT connector. Thirty seven grounds are included for power and high speed signal returns, as well as 21 power pins supplying power to the module. The additional ground pins for signal returns are connected to ground and are an absolute necessity as interface speed increase. Power control adheres to industry standard ACPI “ATX style” signaling conventions. This eases module power control plus ensures that all voltages necessary except that the standard 3.3V, +5V and +12V supplies are generated on the processor module. This further minimizes issues with power supply sizing and stability that occur when passing these processorspecific power rails across a connector. Suspend and battery voltages are also provided to the connector.

Figure 3: The Intel® Atom™ processor powers the compact, 62x75mm, COMIT SFF-COM module.

Is the module size dictated by the COMIT specification?

COMIT is the enabling connectorization technology and pin definitions, not any specific form factor or size. Beyond any standard sizes defined in specifications by the SFF-SIG, COMIT can be used in any custom application requiring its unique combination of features and its rugged, fast connector technology. Currently, two module sizes have been defined. 62x75mm - coined SFF-COM™ specifically for a COM module that is the correct size to modularize the CPU on embedded SBC’s like EBX, EPIC and ISM. At 90x96mm, the ISM™ or Industry Standard Module size has also been defined as a COMIT processor module form factor dubbed COMIT-ISM™ to support higher power processor and larger chipset packages that will not fit on either SFF-COM sized modules or on ISM sized SBCs. This allows a designer to choose a COMITbased processor module to match their performance and price goals.

Product Availability

At the 2009 Boston Embedded Systems Conference, the first products were introduced based upon the Intel® Atom™ processors Z530 and Z510. Pictured in Figure 3 is a 62x75mm module with the COMIT connector at the top of the board. It includes either a 1.1 or 1.6 GHz processor, 512KB or 1 GB of onboard SDRAM, microSD slot, and System Controller Hub. Also, two PCIe x1 channels, four USB 2.0 ports, PATA interface, audio, video, LPC, SPI, and SMBus. This module will operate from -40° to +70°C for applications in industrial and fanless environments.

Figure 4: A WinSystems’ EBX-size single board computer with an Intel® Atom™ processor-based COMIT module installed

COMIT-based modules open a new world of embedded computing opportunities using the newest ultra-mobile Intel® chipsets for a wide range of applications including industrial control, medical, security, transportation, communications, and Mil/COTS. Also, the first EBX baseboard with a COMIT module was introduced at ESC Boston. Shown in Figure 4, it is called the EBC-Z530-G. This board can serve as either an evaluation/development platform for a COMIT module or as an embedded SBC. A 1.6 GHz Intel® Atom™ processor-based COMIT-enabled module is onboard which serves as the processor. The baseboard has interface electronics providing CRT and LVDS flat panel support, a CompactFlash socket, SD memory socket, and miniPCIe socket (for wireless add-in modules). I/O includes two Gigabyte Ethernet channels, four USB 2.0 ports, four RS-232/422/485 serial channels, optional CAN bus, 48 lines of digital I/O, IDE interface, PS/2 mouse controller, LPT, HD audio plus SUMIT and PC/104 expansion connectors on a board that measures 146mm x 203mm.

About the SFF-SIG

The SFF-SIG is an international organization devoted to identifying, creating, and promoting standards that help electronics system and device manufacturers and integrators move to small form factor technologies and building blocks in their products in order to protect their investments over the long term. A free, downloadable copy of the COMIT Specification is available at http://www.sff-sig.org/comit.html

Robert Burckle is Vice-President of WinSystems, Inc which is based in Arlington, TX. He has more than 30 years of experience in embedded computing and holds Bachelors and Masters degrees in Electrical Engineering from the University of Louisville and a MBA from the University of North Texas.

Contact Information

WinSystems, Inc.
715 Stadium Drive
Arlington, Texas 76011
817-274-7553 Telephone
817-548-1358 Fax