A new enhancement to VME was announced at the Real Time Computer Show and Conference, January 15-17, 1997, in Santa Clara, California.

The Impact of New Backplane Technology on the VME64x Draft Standard

SCOTTSDALE, AZ, January 31, 1997 -- The VME320 backplane announced by Arizona Digital and Bustronics represents a major advance in backplane technology that will allow the continued evolution of VME technology well into the 21st century. Arizona Digital and Bustronics claim to have developed a backplane that allows reliable data transfer rates of 320 Mbytes/second and above. A demonstration of the backplane was shown at the recent Real Time Computer Conference in Santa Clara, CA, where data was transferred across the 320 backplane from a frame buffer to a video board and then displayed on a monitor in real time. Such a backplane could be the enabling technology for the enhanced data performance goals of the VME64x draft standard.

VME64x Draft Standard
The VME64x draft standard has been in development for over two years and provides a number of critical enhancements to the ANSI/VITA 1-1994, VME64 standard. Key to the VME64x draft standard is a new 160 pin DIN-like connector that is totally interoperable with the previous 96 pin DIN connector. Two additional rows of 32 pins each have been added to the connector. Being interoperable, a 96 pin module can plug into a 160 pin connector backplane and vice versa. These two new rows provide additional grounds, voltages, and new features such as geographical addressing for new application requirements, besides providing a host of new user defined pins. The VME64x draft standard addresses the need for heighten electro-magnetic compatibility (EMC) to meet tough new electro-magnetic interference (EMI) standards. Another customer requested feature is the need for slot specific keying. A field installable method has been worked out that allows for up to 4096 different keying possibilities.

VME to VME64
To double VME performance, the data transfer width was increased from 32 bits to 64 bits in the early 1990's via VME64. During block transfers data is multiplexed onto the address lines providing for 64 bits of data on each transaction rather than only 32.

2eVME
As part of the VME64x draft standard a new protocol has been developed titled 2eVME for "two edge VME" protocol. The goal of this protocol is to again double the VME data transfer rate by transferring data on each edge rather than on a single transition. Using two edge protocols allows a 2x performance improvement while maintaining the same clocking frequency. In order to work, both falling and rising edges must be monotonic and incident wave switching must be attained. In the past it was hard to insure incident wave switching because of driver characteristics and the required termination network. Simulations carried out by a group of VME manufacturers indicate that incident wave switching can be attained if the rise time of the drivers can be slowed to 5 nsec. Slowing the rise time reduces induced noise and also improves signal reliability. To achieve this rise time a network of 66 ohms with a 270 nh inductor can be used.

Enter the 320 Backplane
However, the technology used in the VME320 backplane provides an alternative to slowing the rise time and adding a network to each driver. Currently a group within the VITA Standards Organization is investigating the impact the VME320 backplane will have on the 2eVME protocol. At the very least it appears the VME320 backplane may support 2eVME without additional components, but more work needs to be done before a final conclusion can be drawn. In addition the group is investigating synchronous data transfer methods that could be used in conjunction with 2eVME to provide data transfer rates in excess of the original goals of 2eVME. Whereas the original goals of the VME64x draft standard were constrained to maintaining the same clocking frequency, the 320 backplane has apparently removed those constraints and allowed faster protocols to be investigated.

Still the One
VME, the bus protocol, that started it all back in the early 1980's is still going strong as we near the 21st century. The original developers of VME can be proud of their efforts. Their spirit lives on! Certain key features of VME have allowed it to evolve with technology and VME continues to be the premiere embedded real-time bus architecture with a world wide market of 1.5 billion dollars. The VITA Standards Organization meets every two months and minutes are published after every meeting. Follow the developments on this web site under the VSO Activites section.

John Rynearson
VITA Technical Director

Above: VITA contributed to the industry awareness of 'VME320' during the Real Time Show and Conference. 'Silver bullet' keychains, badges and booth display were visible on the show floor as was Executive Director, Ray Alderman- shown in full western attire.

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