Hi,

Look for something like the MAXIM MAX242 which has a shutdown mode
putting the transmitter in tri-state but keeping the receiver active.

Datasheet at http://209.1.238.250/arpdf/1798.pdf


Mike.

Joe McCauley wrote:
>
> Hi,
>
> I need to communicate over tens of meters with several PICs (16f874) using
> RS232. The idea is that all devices listen for their address and then accept
> commands to recieve or send data packets. I am looking for a driver chip to
> allow me to do this. Ideally the driver should be able to recieve data at
> any time, but only turn on its output when data has to be sent by that
> device. (avoiding bus contention)
> Cost is an issue.
> On a slightly OT note, does any one know how to use an MSComm control in
> Visual Basic to send 9 bits of data? I was planning to use the 9 bit mode in
> the PIC to distinguish between address and data.
>
> Thanks for any help
>
> Joe