Lpc2000

> Ha!  Welcome to RS485.  It is a bit more complex than it looks.
>
> I don't know why you believe that you needs such precise control over
> the relationship of TXD/RXD and the DIRection?  By it's very nature,
> RS485 communications over twisted pair require that the line be
> precharged before it can be used.
>
> Think about it, the wire is floating electrically, any stray magnetic or
> electrical field can induce a blip into the "dead" wire.  By first
> turning the direction to Transmit, then hold that for a few TX char
> times, it allows the uart at the RX side to settle down.  The uart that
> the RX side may have heard a blip and is in the process of receiving a
> erroneous char.  Once you precharge the line, send your data, then HOLD
> the carrier (direction) until the last char has been sent and then flip
> the line back to RX mode.
>
> Most of the systems I've seen / worked on have a "quiet" line floating
> as the units are all listening for some other unit to speak.
>
> TomW

Hello Tom.
I am right now working with RS485. I had most of the problems (the last 3 
days) with a good way to make the computer transmit over RS485. I tried with 
RTS controling the DE pin, but it was a nightmare. I am drawing a board right 
now with a 555 that is trigged by RTS and every low level on the TX line to 
control the state of DE.

You talked about a precharge, do you know what are a safe time to precharge 
the line?