Acorn Econet - test-drb@ccmp.vtda.org

8 Oct 2003

On Oct 8, 21:24, Tony Duell wrote:

...
  I see... Since I intend to start out by linking the
ACW to a couple of
...
  other machines (one acting as a fileserver), all on
the same bench, I
 assume I can get away with just about any cable :-) 
Well, I'd not use tinsel cable or damp string (even with salt) but
apart from that...

...
  Actually, I am not sure the card in the Atom is a real
Acorn one. It's
...
  the same circuit, and the same layout, but the PCB is
not solder-masked.
...
  It may be a copy.. 
Possibly.  HCCS made some, I think.

...
    The B+ (in the ACW) has PCB positions for the
collision-detect  comparator
  chip, etc, but they're not fitted.... 
 It's worth doing. 
 OK, I'll add them sometime. It's farily obvious what to do from the
 schematics (I have those). Will the software make use of the collision
...
  detect circuitry, or do I need a particular version of
the NFS ROM? 
No, all the ROMs I know of can handle that.

...
  I wondered if you could do that... Alas I don't
have the official Acorn
...
  schematics for the clock and terminator, so while I
can see the empty
 places for termination resistors on the clock PCB, and while I can make a
...
  guess as to the values, I don't know if said guess
is good. Do you happen
...
  to have a parts list or schematic? 
I have a schematic around here somewhere.  [hunts through directories
on nearby machine]  Ah, that one's for the passive (DIN plug) one:

A three-resistor divider chain, 1K0 at the top, 220R in the middle, 1K0
at the bottom, connected to ground (pin 2).  Data+ (pin 1) goes to the
to of the 220R, Data- (pin 4) goes to the lower end.  A pair of 56R
resistors goes from each of Clock+ (pin 3) and Clock- (pin 5) to the
top of the upper 1K0.  A 10 uF electrolytic goes from the junction of
the 2 x 56R and upper 1K0, to ground.

Jules Richardson has my pile of paper schematics, and I think that's
where the other one is :-(

Oh, but of course I have the box itself.  Here we are:

C1, C2:  10uF 10V
C3:      10nF ceramic
R1, R2:  56R
R3:      100R
R7:      470R
D1:      OA47 (anything with a low Vf, eg a Schottky diode, should do)
IC3:     LM7805
LED1:    any old red LED (or you might want to change the colour for
the combined clock/terminator unit)
SK1:     5-pin 180deg PCB DIN socket
SK2:     power jack

Fit wire links at LK1, LK2, LK3.

Do you needs the component values for the collision-detect circuitry as
well?  I've got B and B+ diagrams here, which show them.

...
  Well, I am a great beleiver in proper termination
(resistors are cheap,
...
  my time in tracing bad signals isn't). So, for
example, while I might run
...
  a Unibus for testing with only one terminator (if
it's just one
 backplane, say), any machine that I use will have a terminator at each
...
  end. And I'll do the same with Econet. 
I should hope so too!  You'll see a difference if you remove a
terminator from an Econet of any useful size -- used to be a real
problem in scholls, if they used DIN-plug terminators (kids used to
"borrow" them).

-- 
Pete						Peter Turnbull
						Network Manager
						University of York