By Kim Rubin
Mezzanines are about space. The purpose of these popular, small daughtercard is to implement the highest amount of input/output and processing functionality into as small a space as possible. The fundamental measure of success of any mezzanine standard is how well it meets this primary need for functional density.
Standards have evolved to address convenience, time, and cost. If we had the luxury of unlimited budgets and unlimited time for every program, we could custom design all of our electronics from scratch specifically for those programs.
The realities of cost issues and time pressures, however, force us to solve our design challenges with standard products and interfaces, and with off-the-shelf products that support those standards. The success of a standard is how well it delivers the solutions that we need. Typically, a good measure of success for a standard is the number of vendors supporting it with products.
A new mezzanine circuit card standard has emerged that is ready to be put to the "reality test." The new mezzanine is called PC-MIP, which came about through a collaboration of experts from SBS Greenspring in Menlo Park, Calif., and MEN Mikro Elektronik GmbH in Nuremberg, Germany. SBS Greenspring is well known as the inventor and largest vendor of IndustryPack I/O mezzanine cards, and MEN is the creator of the standard M-Module mezzanine card for VME printed circuit boards, which have sold well in Europe, particularly in Germany.
Officials of the Motorola Computer Group in Tempe, Ariz., joined SBS Greenspring and MEN to sponsor a standards task group under the American National Standards Institute/VME International Trade Association standards organization. Leaders of the task group have the working number "VITA 29." They have an e-mail reflector, and are finishing the written draft standard. Representatives of several companies, including the sponsors, are creating the first PC-MIP products.
The world needs another mezzanine standard because PC-MIP provides capabilities that no other mezzanine can offer, including unmatched density. Six modules easily fit on a single-slot VME or Compact PCI host board.
PC-MIP mezzanine cards use the PCI bus as the logical interface, which provides high bandwidth - 132 megabytes per second - and also access to large and growing family of inexpensive single-chip interfaces.
The availability of compatible, low-cost mezzanine cards are crucial to the success of the PC-MIP standard. Framers of the standard conceived of these modules to support low-cost implementation, as well as high density. This is in stark contrast to PCI mezzanine cards - better known as PMCs, which measure 75 by 100 millimeters. These mezzanine cards not only are quite large, but also require machined mechanical components.
PC-MIPs, which measure 42 square centimeters, are 62 percent smaller than PMCs. Since PC board manufacturers price them by size, this means basic functions such as Fast Ethernet, flash memory, or data acquisition will be of correspondingly lower cost. PC-MIP`s 100 percent surface-mount construction also contributes to lower manufacturing costs than PMCs. PC-MIP joins several well-established mezzanine I/O modules in the global marketplace. It provides state-of-the-art mezzanine functionality, with small size, high bandwidth, and low cost.
Several features of PC-MIP that are not available on any other mezzanine card are standard on PC-MIP. For example, all PCI-MIP modules include captive injector/`ejector hardware to facilitate easy, reliable installation and removal.
PC-MIP is the only module to accommodate both types of the most popular I/O. PC-MIP type 1 addresses flexible I/O which routes out the back panel of VME and CompactPCI chassis, while PC-MIP type 2 addresses front-panel I/O with integral connectors on the mezzanine. Type 1 and type 2 cards are compatible. Avionics and military customers, for example, usually prefer back-panel I/O. Research-oriented and low-volume customers generally prefer the convenience of front-panel I/O.
PC-MIP designers paid close attention to the number of mechanical options and electrical variations, and adhered strictly to the PCI 2.1 specification to ensure compatibility among PC-MIP cards. Not all PCI-based mezzanines can make this claim. For example, the IEEE-P1386 Common Mezzanine Card standard lists 32 combinations of size, height, and voltage, as well as 15 other standards documents. PC-MIPs, on the other hand, are as easy to design as they are to use for engineers who prefer to design their own specialized modules.
The type 1 back-panel PC-MIP module measures 47 by 90 millimeters, and the type 2 front-panel card measures 47 by 99 millimeters. Two 64-pin SMT connectors provide the PCI bus, complete with 22 ground pins and 25 power pins. A third identical 64 pin connector provides 50 lines of I/O and 14 additional grounds. The large number of ground pins on the perimeter of the module assures high-frequency performance as well as ease of passing strict CE and FCC emissions requirements. This attribute is also unique among mezzanine standards.
If density is the measure of success, PC-MIP shows sure signs of being a winner, as the following density examples show:
- four independent FP connectors on a VME or CompactPCI card;
- 300 lines of I/O on a VME card;
- 300 lines of I/O on a CompactPCI card;
- 300 lines of I/O on a full-size desktop PCI card;
- 150 lines of I/O on a half-size short desktop PCI card;
- 150 lines of I/O on a 3U VME card;
- 150 lines of I/O on a 3U CompactPCI card; and
- 150 lines of I/O on a PLC form factor (Allen-Bradley Open Controller).
The PCI bus as the basis of PC-MIP provides not only access to low-cost standard chips, but also highly integrated and tightly coupled high-end functions such as 3D graphics, DSP, and ATM. Since processors as well as all manner of bus-mastering communications interfaces can easily be implemented today with PCI-interfaced silicon, customers using PC-MIP modules will be equipped to build high-performance, scaleable systems out of standard hardware and software. One example could be a very-high-bandwidth customized communication engine that is not dependent on the host processor or host bus for either bandwidth or processing power.
The vast capabilities of the PC-MIP mezzanine module and the emerging standard behind it justify the motivations of the PC-MIP creators to provide real-world solutions with extended functional density, enhanced compatibility, and low-cost implementation.
Kim Rubin is chief technical officer of the SBS Technologies Computer Group in Menlo Park, Calif., a family of four SBS Technologies operating divisions specializing in board-level CPU and I/O boards, industrial PC enclosures, and software. Prior to taking this position, Mr. Rubin served as executive vice president and chief technical officer at SBS GreenSpring Modular I/O in Menlo Park, Calif. He is considered to the inventor of IndustryPack mezzanine I/O modules, which are now recognized by the ANSI standard, "ANSI/VITA 4-1995, IP Modules," which receive support from more than 120 companies worldwide. Prior to joining SBS GreenSpring, Rubin was U.S. director of engineering for Force Computers in San Jose, Calif. He is a graduate of the University of California at Berkeley (EECS, 1975) and occasionally lectures at Stanford University. Rubin`s e-mail address is [email protected].