>
> To make a long story short, we since have concluded that the most likely
> problem with the CEBAF configuration is the ARCNET cable length between
> mainframes and/or the host controller. This solution was first considered in
> light of the type of testing done at LeCroy where standard cable lengths of
> six feet are used for convenience. All of the CEBAF 1458's are
> interconnected with cables of approximately three feet (possibly less).
> Three feet is the proper minimum length for RG-62 (90 Ohm) cables according
> to the 1458 user's guide and other ARCNET interface reference material from
> SMC.
>
> We have recommended that Hall B try using six foot cables between mainframes
> to see if this fixes the hangup problem.
>
> The following is a list of facts which support to the theory that the
> hangups are related to the cable lengths. These were realized after we had
> completed our visit.
> 1) The monitor loop testing done on site (mentioned earlier) was at
> the end of a six foot cable.
> 2) Hangups observed on 2/21 occured only after the mainframe closest
> to the VME/ARCNET controller was connected onto the net. In this
> configuration, the closet mainframe was connected onto the network with
> cables of 3 feet (possibly less) between the controller and the next mainframe.
> 3) Prior to connecting the closest mainframe, the controller
> to-next-node cable distance was approximately 6 feet when no failures were
> observed.
> 4) Hall B personnel have since inter-connected their mainframes with
> six foot cables and have yet to report any ARCNET hangups as previously
> observed.
>
> The manual for the SMC ARCNET controller card used in the 1458 has a number of
> interconnection rules for various cable types. The minimum length for the
> BNC bus configuration (used with the 1458) is listed as three feet.
> Although on a later page in the same manual a six foot minimum length is
> given for twisted pair cables. I am presently trying to contact SMC for
> further clarification on the sensitivity to to cable distance between nodes.
>
> To further support debugging, we requested that they create an active log of
> the last 10 commands sent to a 1458 mainframe and that this log be dumped
> when they observe any problems.
>
> We also recommended that their standard ARCNET reset procedures include a
> sequence of ARCNET receive commands to empty out any backup command
> responses from a mainframe prior to sending additional commands.
>
> Before we considered the cable length to be an issue. We suggested that they
> check that their mainframes keep proper date and time since we have observed
> some mainframe motherboards to lose their date/time after some period of
> operation. (This is currently believed to be a hardware problem for some
> motherboards.) The idea here was to correlate this date/time loss with an
> ARCNET hangup.
>
> Mike Green
> Mike_G@pisun.lecroy.com
> LRS Engineering
> LeCroy Corporation (LCRY)
>
>
>