Date   : Sun, 28 Mar 2004 13:52:02 +0200 (BST)
From   : Johan Heuseveldt <johan@...>
Subject: Re: MDFS incomplete startup

Hi Pete,

On Sun 28 Mar, Pete Turnbull wrote:
> On Mar 27, 20:06, Johan Heuseveldt wrote:
> 
> > I don't use terminators other than the internal ones on the machines
> > in use. If the network is smaller than ten meters, no external
> > termination is necessary. That's an Acorn remark from somewhere out of
> > the documentation, probably FileStore.
> > Mine is about 3 meters. A Master 128 at one side, the SJResearch Econet
> > Bridge at the other and the MDFS in between (but not in the middle: the
> > two cables are about 2m and 1m).
> 
> You really should use terminators.  There are no terminators on any
> normal Econet interface, and you *will* get reflections from unterminated
> lines.  You may not notice on such a short network, partly because the
> protocol is robust, but mostly because the network is short compared to the
> pulse lengths.  Nevertheless, I bet your network will be capable of
> performing better if you put the correct termination on each end.

Actually there are terminators on board: All lines have a serial
resistor of 100K and pull up of 10K.

Compare the connection to the net with Ethernet Coax, using T-pieces. But
the 'T-piece' is not at the machine side but at the network side, leaving
some length which cannot benefit fully from the main network termination.
Normal BBC connection leads are 1m to 1.20m. The connection lead for the
Risc PC is almost 2m!.

So, every connection lead between net and machine is a small
subnetconnection which is not part of the main net in this context of
termination. The network side is already ok, but then the machine's side
needs proper termination too!!
So a small termination at the machine side /is/ necessary!

It is small enough to prevent too much load on the network cable with many
machines connected. So termination in the machine is as small as possible to
allow for some length of the connection lead.

Some day I'll find the remark about this, and let you know! :-)

> BTW, phone cable *is* twisted, just not nearly as tightly as proper
> Econet cable, or Cat 3/4/5/5e.

It is/was very simple cable, also usable for telephone purposes, and not
twisted at all. Very cheap. Indeed I was surprised it worked. I set the
clock box to 500 kHz and the A5000 bahaved very well! :-)

I also used many meters between the connection boxes, leaving all the
cable at random under the table and was messy to see. But it worked! But
was within 10 (ten) meters on both sides of the clock box.
Of course I need to slow down to 200kHz for the Beebs!
 
And, not at least, It have been working reliably just a few weeks ago.

BTW : Floppy disc drives are OK. Checked on the Master.



I noticed that the temperature of the MC146818 remains cold. So atm I'm
suspicious about this clock chip. While removing/inserting this chip, you
can't disconnect the backup power. Normally this is a bad thing to do???

So I need to check this too.



Thanks for your co-operative thinking Pete!
In fact all of you! Thanks


greetings,
Johan

-- 
Johan Heuseveldt <johan@...              >
  aka  waarland

  The best place is a Riscy place
 
People who live in stone houses shouldn't throw glasses.