> Hi
>
> I am student of the faculty of Electronics in Poland and want to build RS232
 to RS485 converter in order to use it as my home LAN extension via one twisted
 pair wire to my friend's home for Internet >
> 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 >
> RXD TXD RXD TXD ....
>
> Or maybe RTS/CTS signals must be used to switch between receive/transmit mode
 and PC software (like port driver) takes care of it?
> But what will happen for instance during initial negotiation when both
 computers will want to transmit or receive simultaneously? It must be simple
 null modem but based on RS485. No drivers will not >
> I write software in Assembly language and I have built some good controllers
 and measuring devices with AD converters, displays etc.. I use PC everyday but
 such problem made me crazy.
> I know that my problem is very funny, and basic in general but please give me
 some piece of information or URL to find it?
>
> Please help
>
> Juliusz
>

Hello Juliusz

As somebody already has pointed out to you RS485 is only half
duplex with 2 wires (1 pair). To make it full duplex use 4 wires
(2 pairs). If there are only 2 nodes this is the same as two
RS422 connections.

Also, you must have some kind of reference wire connected between
the two nodes so the voltage difference between the inputlines and
the nodes ground doesn't get too big. This can be the shield of
cable. It might be a good idea to isolate the RS422/485 side of the
nodes with an isolated DC/DC converter and optocouplers.

--------------------------------
Ruben Jvnsson
maxruben@mail.bip.net
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