The Evolution of Eurocard based Architecture from VMEbus to AdvancedTCA and beyond
19” Technology and associated Eurocard mechanics still play a significant role in the Electronic packaging industry. Their continued success can in large part be attributed to the steady and inexorable progress made by the bus based architectures like the VMEbus, VXIbus, cPCI bus to the bus agnostic Fabric architectures like cPSB, StarFabric, ACTA etc.
There is no gainsaying the fact that the successful development and deployment of these “open standards” based bus architectures has raised the awareness of major market segments like Telecom (Networking equipment, Media Gateways, Computer Telephony etc) and Military (Missile tracking and guidance, Avionics, Sonar, Radar etc) to the advantages of leveraging such standards in their product designs. This article will briefly trace the evolution of these architectures ever since the
introduction of the Versabus, spurred by the insatiable demands for higher speed, bandwidth, scalability, reliability and greater flexibility in connectivity.
The advent of the microprocessor created the foundation for the microcomputer bus industry. The VERSAbus by Motorola in 1979 based on the 68000 microprocessor formed the electrical basis for the new VMEbus (Versa Module Eurocard) along with the preexisting Eurocard mechanics.
Eurocard is a term that collectively represents the products based on the DIN 41612 and IEC 603-2 connector standards, the IEEE 1101 Printed circuit boards standards and the DIN 41494 and IEC 297-2 rack standards. All the mechanical hardware were readily available and proven to be robust. The VMEbus was born in 1981 as a result of the joint efforts of Motorola, Philips/Signetics and Mostek. Subsequently it was adopted as a standard by IEEE (IEEE 1014- 1987) and IEC. At this point the VMEbus was a 16 bit, easily upgradeable, microprocessor independent, non-proprietary bus standard with a proven mechanical form factor that any vendor could use to make interoperable and compatible products. In the years since, it has proven to be a defacto standard and the pioneering joint development efforts has been repeatedly and successfully adopted to drive new emerging standards and specifications to this day. The unprecedented success of VMEbus architecture was in no small part due to the Robust Eurocardform factor.
As technology progressed with faster boards and chips, the necessity to upgrade from 16 bit, 40 Mbytes/sec to 32- bit (3U) and 64-bit (6U) with twice the bandwidth (80 Mbytes/sec) caused the VMEbus specification to be revised through IEEE 1014-1987 and ANSI/VITA 1-1994. The latter is also referred to as the VME64. This improvement along with Automatic ‘Plug n Play” feature, Auto Slot ID and a host of others served to enhance the popularity of VMEbus in Embedded applications. The next major revision to the spec was the ANSI/VITA 1.1-1997, aka VMEbus Extensions or VME64X . This added new capabilities like a new 160 pin connector, a 95 pin P0/J0 connector for additional I/O, 3.3V power plane, 160Mbytes/sec bandwidth, more 5V power, Rear plug-in units, Hot swap capability, EMC front panels with Injector-Ejector handles and Geographical addressing. It is no secret that the VMEbus extensions also extended the life of VME. The Military applications where VME had a strong foot hold because of its backward compatibility, longer life span, etc were nonetheless beginning to get constrained by limited speeds, bandwidth and I/O for which VME64X was the perfect answer. VME64/64X has also proven to be an unqualified success in ATR (Air transport Rack) type enclosures with conduction cooling. Another improvement to the speed of the VMEbus was the announcement of VME320 by Bustronic Corp and Arizona Digital that made a data transfer rate of 320Mbytes/sec possible using a ‘Star’ interconnection scheme. Finally, after 20 years of yeomen service to the industry, VME brings a promise of even higher performance with the introduction early this year of the VME Renaissance by Motorola. Based on the 2eSST protocol, the VME Renaissance should provide a vastly improved board to board interconnect capability and is “intended to herald an era
of profound innovation and performance improvement while maintaining backward compatibility
and protecting existing customer investments”.
In the mid to late nineties, VME was facing competition from a new emerging bus based
architecture called compactPCI. This was based on the 2mm connector standard and the IEEE
1101.10/11 mechanicals with PCI being the core electrical portion. PCIbus was a proven bus
with an enormous installed base in different market segments like telecom, industrial automation,
etc. The compactPCI architecture could also leverage off the lower cost, widely available PCI
silicon and the omnipresent WinTel (Windows/ Intel) architecture. A 64-bit implementation could
boast a data transfer rate of 533Mbytes/sec. Like the way VITA promoted VME successfully,
cPCI was effectively promoted by a group of PCI manufacturers under PICMG. PICMG
released a series of specifications in the late nineties that addressed critical requirements in the
Telecommunications industry like Hot swap and five nines availability (99.999). PICMG 2.1
(Hotswap), PICMG 2.5 (H110 Telephony bus), PICMG 2.7 (Dual system slot) and PICMG 2.9 (System
management bus) were some of the specifications that made using cPCI bus a compelling reason for new
products catering to computer telephony, VoIP and a myriad other applications. With a soaring demand for
more speed and bandwidth fueled by the Internet boom, cPCI became extremely popular with its open
standard that helped speed the “time to market” for new entrants in the telecom arena. The Eurocard form
factors of 6U by 160mm for front line cards and 6u x 80mm for rear transition cards was tailor made for
platform providers to develop rackmount equipment that met the NEBS criteria for 300mm depth as well as
cable management. – Important considerations for Central Office applications.
Eventually, the slot limitations of compactPCI and the bottlenecks to higher data transfer rates (a must for
I/O intensive applications) posed by bus based architecture prompted the foray into high speed serial buses
and Switched fabric architectures in the last couple of years. Specifications like the PICMG 2.16 for packet
switching backplanes (cPSB) and PICMG 2.17 (aka StarFabric) draft specification are beginning to draw
attention with the cPSB taking a lead with a lot of compliant hardware already available in the industry.
Since these were all based on the PICMG core 2.0 cPCI specification, the form factor remained 6u x
160mm (Eurocard). With the advent of high speed connectors by leading connector manufacturers like
Amp/Tyco, Teradyne, Erni and FCI, high speed Hybrid backplanes employing fabric for the dataplane and
a traditional bus like VME or cPCI for the control plane became an alternative option for many proprietary
product designs wherein the movement of large blocks of data was not a prerequisite. The use of a reliable
bus like VME mitigated the risks associated with fabrics while leveraging their higher performance levels
for high end applications Switch-fabric interconnection is also preferable for high availability applications
due to their self- healing features.
In late 2001, PICMG formed a new committee to develop a new series of specifications aimed at the next
generation of Telecom requirements. The 3.X series was renamed as Advanced Telecom Compute
Architecture or Advanced TCA and an 8U Eurocard was chosen as the form factor of choice. The draft
specification calls out for an 8U x 280mm front boards and 6U x 60mm rear boards. Thus the Eurocard
mechanics continues to exert its influence as the form factor of choice in emerging technologies. The
advantages it brings to electronic packaging in addition to the ruggedness and precision are the ability of
leading packaging vendors like Elma Electronic Inc to leverage off existing hardware and platform designs
and put forth a compliant economic solution in the shortest time possible.
Ram Rajan
VP Engineering
Elma Electronic Inc. |
