jas@proteon.com (John A. Shriver) (07/05/89)
Yes, at least the original Sun VME 3->2 adapter caused boards using it to fail to meet the VMEbus specifications. The problem is that the wires on the adapter's PC board use up all of the "stub" budget for cards on the VMEbus. All transceivers have to be within some very small distance (about 2 inches) of the pins on the board. I think Sun redesigned the adapter so that the etch was shorter, but it still could cause problems with reflections. (It might also generate some crosstalk.) The timing on the VMEbus is very tight, so one has to watch the transmission line stuff carefully. Of course, the adapter works fine with Sun's boards, but the SCSI controllers are not high-speed 32-bit DMA devices. There are third-party adapters which do not have any connectors, and are just a peice of plastic that attaches to the edges of the board, to bring it up to 9u size.