Use four wires, one pair for TX and another pair for RX. This way you
have full duplex and do not have to worry about switching at all. In the
software side you can use it as a regular RS-232 without handshake.

Best regards,
Alexandre Guimaraes
Microset Eletronica Ltda
alexg@iis.com.br


> Hardware is very clear for such purpose but I can't find information how
to convert RXD > and TXD ? two signals into 1 signal of the current loop. I
mean I don't know how to
> create protocol between my 485 modems? Are RXD and TXD multiplexed
(switched) every
> transmitted/received byte like
>
> RXD TXD RXD TXD ....