Re: more net notes...

From: Ethan Dicks (
Date: 2000-07-27 08:50:13

--- Larry Anderson <> wrote:
> After a little thought about the throughput of the network (ok, I havent
> got 'that far', but I like to plan ahead), I am thinking we can get
> increased speed with more data moved between nodes and less transitions
> (input to output) than going around the ring with each node's data
> (packet->in/out/in/out/in/out ->next packet)...
> Of course this got me excited about file serives, file transfers,
> application services and the like but the main drawback to this topology
> is if one computer drops out (like when we have to cycle the power to
> exit a game), the net will need to automatically reset and recover
> somehow (after the computer comes back on and the NOS is re-loaded on
> it...). This is where ethernet has the advantage as you can join and
> unjoin from the network without upsetting the data flow, as everyone
> taps into a common 'ether'.

Have you ever worked with FDDI or Arcnet or any token-based networking
scheme?  If a token is lost, there is always a mechanism for regenerating
the token.  Can't go around rebooting servers in a production environment
just because they lost connectivity for a moment.

Depending on what you really want to do, there is a one-chip ArcNET solution
that is as easy to attach to a 6502 as an ACIA - the COM20020.  Dave Haynie
tried to design it into several Amiga models, only to have management remove
it due to cost.  His idea was self-terminating RCA jacks (like the ones in
the front of modern VCRs for audio/video - they short out if there is no
plug installed (with a termination resistor in the Amiga's case), or if you
insert a cable, the internal short is opened and the connector passes data.
A low-tech no terminator solution.  Think of LocalTalk adapters but cheaper.

If you use an RS-485 driver chip (8 pins, <$1 each), it's possible to build
a twisted-pair, multidrop ArcNET network.  The COM20020 has built-in buffer
RAM, enough for a full packet.  You don't have the same problem with data 
underruns because of how ArcNET works.  It's not broadcast like Ethernet.

It all depends on what you are really trying to do here, but if a hardware
solution is called for, consider this chip.  There's a schematic I worked
on *years* ago (1987?) for an Amiga parallel port ArcNET adapter.  I never
built one and we never wrote drivers, but I got questions about it for several
years.  I'm pretty sure it's on AmiNET.  A search for pocket.lzh might turn
it up.  It's not much more than a COM chip, a line driver and a crystal.
Easy as pie.  The software is another matter entirely.  You'd still have to
implement some kind of protcol stack for the higher layers, but at least
you would be able to get bits from one box to the next from the get go.

Other schemes might make more sense if they only require a cable and possibly
a line buffer.  Depends on the goals.


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