I'm running a network of instruments using a 4 wire RS-485 scheme,
where there is a single master and multiple slaves. All the slave
receivers connect to the master transmitter, and all the slave
transmitters connect to the master receiver. I have logic that
automatically switches all the slaves into receive mode whenever the
master drives it's transmit signal active.

All the slaves contain PICs (18fxxxx)  and use the UART to implement the RS-485.

I Now want to make a different version that operates as a party line,
with all transmitters and receivers connected together. To do so, each
node has to know how to turn off its transmitter as soon as it has
finished a transmission.

What's the cleanest way, in a PIC, to do this? I think I can't use the
UART Transmit interrupt, because it does not tell you when the last
byte has gone out on the wire. I know I could use a timer but consider
that my solution of last resort. I'm looking for any other ideas that
would let me turn off the transmitter at the earliest possible moment,
as soon as the last transmitted byte is on the wire.
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