> Without any equipment mastering the bus?

In this case I did use a master/slave arrangement.  One of the nodes on
the bus was the master, but all the bus interfaces were electrically
identical.

> Any slave can send packet when the bus is free?

Any slave can electrically drive the bus at any time, but the protocol was
designed to prevent this.  The protocol could also tolerate bus noise, but
performance degraded as noise increased.  In practise dropped packets were
extremely rare, usually just when a slave was hot plugged to or from the
bus.

In this particular scheme, the master polled all the known slaves in a
circular fashion, kind of like how USB works at the lowest level.  At the
higher protocol levels, it did appear like a slave could talk at any time.
There were also mechanism for discovering new slaves being added and
existing ones dropping out.  By the way, the bus mater was a Pentium, and
each slave was a 16C77 (this was before chips like the 16F877 were
available).


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