AVR-Chat

Tom Becker wrote:
>  >> ... Unless you are making a unidirectional
> 
>>>connection, you need at LEAST 3 wires for a proper RS232-C link.  
>>>Ground, TX and RX.
>>
>>That's what i said before, unless the line is half-duplex.
> 
> Do you mean unless the line is simplex?

Yes, for simplex which is one-way only, and half-duplex.

Half duplex is when the ends alternate between being a transmitter
or receiver, using the same wire. You need tri-stateable transmitters
for that, and a software protocol. It's usually less hassle just to
use 3 wires and full duplex for 1:1 connections. For a multidrop
half-duplex network, the tristateable method can be used, but you
need to make your own higher current tristateable rs232 transmitters.
I've done that, but it's not very economical for component count and
RS485 would be better. I've also tried the dominant pull-down method
like i2c and canbus, but then that's hardly rs232 anymore.