Interconnecting classic computers

[Tony Duell]

> > Oh.  How about those assorted daisy-chain schemes using RT11 phone cabl=
> es?
> > I remember the labels reading something like "much less expensive than
> > Ethernet".
> 
> I don't remember running into those,  how were they interfaced?  And used=
>  with=20
> what sort of equipment?

Thypicallyt they were used with IBM-compatible PCs and plugged into the 
serial ports. There were many schemes, but the simplest was something 
like : 



TxD o---->|--------+----------------o Network line
                   |
RxD o--------------+
                   |
DTR o-/\/\/--------+

SG  o-------------------------------o Network ground/common

Some of the better versions had swiches built into the network cale 
connector so that the resistor was only connected on the 'end' 2 machines.

The PC ran special software (oviously). THe DTR line was set -ve, and the 
resistor pulled the DTR line (of all PCs on the network) to -12V. Any 
machine could send data onto the network wire, all machines would then 
receive it. The transmitting machine monitored its own transmission, if 
there was a collision, it didn't see what it expected to see, there was 
then a stnadarrd-tupe of collision recovery.

-tony