Interconnecting classic computers

[Ray Arachelian]

Tony Duell wrote:
> As I think most of you know, I have a fairly diverse collection of 
> classic computers (I suspect some others do too). 
> ...
>   

> Must not make use of any flow control lines on the RS232 port, since some 
> of my machines don't support them.
>
>   
...
> Using classic, or at least repairable, hardwre is a bonus :-)
>
>   
...
> I said 'RS232'. I mean asynchronous serial, of course :-). If somebody 
> has a solution for TTL or 3.3V level serial ports, I can trivially 
> convert the signal levels
>
>   
...
> I've been looking at some of the license-exempt radio modules, but they 
> either are half-duplex or amke use of the flow control lines (typically 
> they buffer <n> bytes internally, then de-assert a flow control line 
> while they pack up that data and send it to the other end). 
>
> Any other ideas?
>
>   

Well, here's what I'd do, which you might not agree with.

I'd wire up as much of the house with plain old CAT-5 cable, and use 
RS232 to CAT-5 conversion plugs.  Then I'd have either a patch panel or 
a terminal server in a central place.  If you need to connect two 
machines, connect an ethernet cable between two ports of the patch 
panel.    Alternatively, if you want them to talk to a modern machine, 
you could either connect the modern machine to the patch panel, or if 
you don't want to bother plugging things in all the time, plug all of 
the ports into the terminal server.

(Finding someone with an old terminal server they're wanting to upgrade 
is a possibility here.  There's also a slightly better option of finding 
classic Hostess multi-port serial cards in ISA form and running them on 
an old XT with say Xenix or an early BSD or Linux and using that as both 
storage server and as a terminal server - you could use the rzsz or 
kermit programs to transfer data for example.  The guys that used to run 
BBS's on PC's might still have these boards in storage for example.)

For areas where you don't want to wire, or can't wire through walls, you 
could go wireless.  I'd use cheap game console ethernet to 802.11b 
converters connected to single port terminal servers - or if there are 
several machines next to each other in an area where you can't wire from 
a distance, a multi-port terminal server.

While you might think that some places might be hard or impossible to 
wire, if you look a bit deeper, you might be able to go through the 
attic, a basement, parallel or through heating/cooling ducts, or even 
outside the house.  In this case, I'd strongly suggest shielded CAT-5.  
This is how I've wired my house for ethernet - I moved in before the 
proliferation of WiFi, so it wasn't a consideration.    I ran shielded 
Cat 5 from the attic which is my computer room all over the house.  
Several lines went down next to the central staircase - just stapled to 
the stairs, down through the basement and into the den and living room, 
others went through the ceiling of the garage into the kitchen and along 
side the walls.  (Besides, despite the low wattage of 802.11b/g, I'm not 
so sure I'd want my kids bombarded with what are essentially 
microwaves.  Had 802.11a been a bit more successful, I might have gone 
that route since it's outside of the resonance frequency of water.)

Perhaps some combination of these things will work best - personally, 
for your specific project I'd favor the CAT-5 with one (or more) ports 
to each machine going to a central patch panel as it offers the highest 
flexibility.  Adding a terminal server or several would depend on how 
much of a need you'd have for it and whether you could find agreeable ones.

Some of the early terminal servers did stupid things such as sending a 
break signal to every port when they were power cycled, these caused 
havoc to Sun machines (and I imagine anything else that dropped into a 
debugger or equivalent) when they received these on their consoles.  
Others won't let you tie two ports together, and others won't work at 
low speeds.  So perhaps a PC with several multi-port serial boards is best.