[Info-vax] retro VMS hardware

[John Wallace]

On Sep 26, 9:56 am, H Vlems <hvl... at freenet.de> wrote:
> On Sep 26, 2:15 am, "Richard B. Gilbert" <rgilber... at comcast.net>
> wrote:
>
>
>
> > glen herrmannsfeldt wrote:
> > > Richard B. Gilbert <rgilber... at comcast.net> wrote:
>
> > >> ISTR a "jig" that fastened on to the cable and guided a drill bit making
> > >> the hole for the "vampire tap".  I never installed any thick-wire
> > >> Ethernet myself and only saw it done once.  Thinwire was a bit more
> > >> convenient and UTP was right around the corner!
>
> > > No jig.  The clamp part goes over the cable first, and is
> > > tightened with the appropriate wrench.  That also includes
> > > two replacable pins that grip through the outer insulation
> > > and into the shield.  Using two allows detecting collisions
> > > while sending.  (Even better would be with two center
> > > conductor taps, but that seems not to be needed.)
>
> > > Then the drill goes through the hole in the clamp such that the
> > > hole has the right depth and position.  The other end of the
> > > drill has the wrench to screw in and tighten the actual tap.
> > > There is a cover to put over it until a transceiver is installed.
>
> > > -- glen
>
> > Seehttp://dictionary.reference.com/browse/jig
>
> > I think it's correct to describe the clamp as a jig since it functions
> > as one.- Hide quoted text -
>
> > - Show quoted text -
>
> ISTR there are two H4000 models, the first model required a jig and
> and a drill to get it installed. The other had the same clamp as the
> H4005.
> The first model was not fit for use with H4005's and thinwire kit,
> there's a heartbeat issue that preventsproper operation in mixed
> configurations.
> Mixed meaning combining 10base5 and 10base2 gear, like fitting a DESPR
> to a 10base5 backbone. There is a hardware fix for the newer H4000
> (which makes it an H4000-AB IIRC). It involves removing one small
> capacitor. The H4005 has this fixed too.
> Hans

Rings a bell here too. My vague recollection is that the original
stuff was Ethernet whereas the later stuff was 802.3, and the relevant
difference in this context is the "carrier detect check
(failure)" (aka heartbeat) circuit. Very vague though.