phil@amdcad.UUCP (Phil Ngai) (08/01/86)
In article <2535@diku.UUCP> krus@diku.UUCP (Lars Povlsen) writes: >>(ask me about how Bridge Comm violates the 802.3 AUI cable connector >>spec, causing AUI connections to be unreliable.) >The connector is a tragedy, agreed, we had a lot of trouble, and >still has. >But since we were only aware of the connection to be unreliable, >not what being the cause, please follow this up. This is pretty hard to describe in words but I will try. The best explanation includes holding the products in your hands and pointing. We have a backpanel with a hole cut in it and a DB-15 connector with ears for mounting. Most people solder connectors into a PC board and then attach a back panel in front of the connector. Let us imagine for a moment that the back panel is not there. The head of a screw mounted in the ears of the DB-15 will be a certain distance from the plane made by the end of the DB-15. If you put a washer on the screw, that will raise the head of the screw and bring it closer to the plane of the connector end. Putting a back panel between the screw and the connector ear has the same effect as a washer. The problem is that the AUI cable has protruding screw heads so the DTE connector's slide latch can engage with the AUI cable's screw heads. When you put the equivalent of a washer on the DTE connector's screws they rise up and interfere with the AUI cable's screws preventing the connectors from fully engaging. This is addressed by the IEEE 802.3 spec which requires "PANEL SHALL BE FLUSH OR BEHIND CONNECTOR FLANGE FOR PROPER SLIDE LATCH OPERATION". (see page 94 of the 802.3 spec) Mounting in front of the connector as BCI does violates the spec and is unreliable. I have looked at a lot of DEC products and they implement this properly even when it required extra engineering to do so. I have brought this to the attention of BCI and their response was that it was a pain to fix and they weren't sure if they would bother. No doubt customer feedback will help them decide whether or not to fix this problem. It's unfortunate that the product couldn't have been properly engineered in the first place and that they take (soon to be if not already) international standards so lightly. If this explanation is unclear please write to me and I will try to clarify. -- Classical music audiences are like ivory soap: 99 44/100 pure (white). Phil Ngai +1 408 749 5720 UUCP: {ucbvax,decwrl,ihnp4,allegra}!amdcad!phil ARPA: amdcad!phil@decwrl.dec.com