::: Area #155 (comp.sys.acorn.networking)
Message: #19091 (Read 4 times, has 0 replies, 2440 bytes)
Date   : Mon Jul 20 09:46:35 1998
From   : "Mark Usher" of fidonet#2:254/27.2
To     : All
Subject: Re: Line jammed - terminators, clocks etc

Hi

OK. The setup is quite simple but a little out of the ordinary. I am
connecting one BBC and one PC with Ecolink card :-)
I have built a circuit board based on the clock / termination in the
advanced user guide with:

term -^-- clock---9 pin-----5pin-5pin-5pin---^----term
      ^            ^          ^    ^    ^    ^
    jumper         PC        BBC  BBC  BBC  jumper

I am getting the clock through fine. There seems to be no problem there. The
BBC though did have the 1770 upgrade fitted, which means removing IC 87 and
fitting a small bridge across two pins. I noticed then that if I
disconnected the econet lead from the BBC it didn't register that there was
"no clock". I refitted this chip and it then functioned fine. Not sure about
the side effects on the DFS here though.

Now, when I start the software on the PC without the Beeb attached it
initialises fine. When the beeb is attached I get a net error message on
initialisation. If I have both attached the BBC finds the clock OK, but if I
try to *NOTIFY myself then I get a Line Jammed message. In fact any network
command brings back a Line Jammed on the BBC.


One thing I am worried about are the terminators as there is no "distance"
involved here, so reflections are going to be pretty minimal. OK I need to
balance things when there is no traffic, so I added the jumpers in case the
terminators are needed. I am getting the clock fine, just get Line Jammed
messages whenever I try to do anything. Obviously the Beeb could also have a
fault on it's ecolink somewhere, but if the clock is working then I would
think the 75159 is OK. I might just try swapping all the socketed chips for
new ones, but I don't hold much hope. Oh, the cable is OK.

One thing I am not sure about is the correct value for termination, ie what
the reading should be across the 1 and 4 lines with a multimeter. I can send
you a schematic if you want to look at the diagram.

Also the clock runs successfully for the PC ecolink at these values.  307K,
230K, 153K, 115K, 76K, 38K. Does this seem about the correct range ?

Appreciate any help / pointers I can get.

Mark






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