Thirty years ago, engineers from Motorola, Mostek, Signetics/Philips, and Thomson-CSF introduced a leading-edge computing bus technology: VMEbus. Since then, supporters have evolved the specification to give VMEbus more performance, richer features, and greater capabilities – all while sticking to the tenant that it must be migration- proof and backwards compatible. No other technology in the computer industry has withstood the test of time while making such a claim. Products designed today can still operate fully in the first backplanes that rolled out in the early 1980s.
Several major enhancements have been made to the VMEbus specification since its introduction in 1981, enabling VMEbus to be as viable as it was 30 years ago.
The first major enhancement was VME64 (1014 Rev. D), introduced in 1991 when Project Authorization Request P1014R for revisions to the VMEbus specification was granted by the Institute of Electrical and Electronic Engineers (IEEE). VME64 raised the theoretical bus speed from 40 MBps to 80 MBps by doubling the number of data lines from 32 to 64. It used an innovative five-row connector that was backward compatible with existing backplanes. Challenges in working with the IEEE led to VITA becoming a member of American National Standards Institute (ANSI) in June of 1992 and gaining accreditation as an ANSI standards body to facilitate development of open architecture standards. In 1994, the VME64 specification became the first VITA specification to receive ANSI approval under ANSI/VITA 1. Minor extensions were approved in 1997 with VME64 Extensions (ANSI/VITA 1.1), commonly termed VME64x. Features included a P0 connector, geographical addressing, voltages pins for 3.3V, a test and maintenance bus, and EMI, ESD, and front-panel keying per IEEE 1101.10.
The second major enhancement was in 1996 when the VME 2eSST protocol was proposed for VMEbus, allowing data transfers synchronously on both clock edges and giving VMEbus the potential to exceed 500 MBps. VME2eSST was ratified in 2003 under ANSI/VITA 1.5.
While nothing new is planned for VMEbus at this time, there is still room for performance improvements in the existing parallel bus architecture without changing the specification. The current VME 2eSST technology will support data rates much higher than any products are capable of today. This can be one of the rare cases where the technology is not outpaced by the products using the technology.
The process for developing and maintaining the VMEbus specification was responsible for many of the processes currently in use by the VITA Standards Organization (VSO), the body of companies responsible for the development and maintenance of nearly 100 embedded computing specifications. Groundbreaking Standards Development Organization (SDO) policies, specifically the handling of ex ante disclosure of patents, have made VITA an organization widely consulted as an SDO. Patent policy changes in Europe and pending changes in the United States and Asia can be directly attributed to the work of VITA.
The company names have come and gone, but the bus still remains viable today and is still being used in new products and winning new design programs. Many suppliers are highly dependent on the staying power of VMEbus-based products to get them through the rough economic times facing the world today.
Visit www.vita.com for a complete history of VMEbus.
For more information, contact Jerry at [email protected].