VME Bus

Posterized VME board

Vero Bicc 3U VME backplane. The orVME 68000 card plugged into the backplane was used in several tannery automation projects, and in an imager project.

Work done from 1988 to 1994


VME bus was defined by Motorola for their 68000 processor. The original Versabus looked like a big Multibus I board with gold finger edge connectors. The DIN41612 connector was a welcome relief. We adopted the pinouts, but not the message passing as per the VIC and VAC chips from Cypress Semiconductor.

VME was a bit complex for simple industrial automation, and the multiprocessor bus was not that easy to work with. The other processors generally mapped dual-ported shared memory in different address spaces on the bus for the other processors. The interface chips also handled DMA into the other processor’s address space. The bus was closely aligned with the 68000 processor signals. Other processors were designed into VME racks, but they often did not used many of the signals — an example was the IDT 3081 MIPS board designed by Algorithmics for Radstone.

We designed several boards that used the VME pinouts, and worked on a PowerPC card with a simplified VME interface in Mecalc 860. VME has gone through several re-incarnations and facelifts, but it remains complex and expensive. The driver for some old Concurrent Technology boards from VxWorks were almost 28 pages of C.

The VME backplane was announced in 1981 with the initial specifications placed into the public domain. With a better edge connector and processor, our transition was away from Multibus to VME.


Vero VME from the front

Vero Bicc 3U 4-slot VME backplane from the front. Note the rows of termination resistors (possibly capacitors also) on either side of the backplane.

Vero VME from the back

Same backplane from the back. The connectors were press-fit. Note the patent notices on the lower left. We tried to look up the USA patent No 432,899, but that was dated July, 1890 and was for a surgical splint. Not much on backplanes there. Anyway, the European Union and Great Britain Patent offices had a patent filed in 1980 by Paul Borril. The patent was GB 2060266 (B). There are later patents on FutureBus terminators also by Paul Borril (1992).

Vero VME strip line

A close-up of the strip-line termination on the Vero Bicc backplane.

Other patents that relate to backplanes are: