In a message dated 97-11-12 17:27:02 EST, you write:

<<
 (2)  Somebody on the list  recently indicated that it was  easy to convert
 from RS232 to RS485, I have no problem at the PIC level but without
 purchasing an expensive RS485 Card for my PC which is  intended  to be the
 master controller in a multi-drop system I am having difficulty in enabling
 the RS485 driver from a standard PC RS232 port while transmitting  and then
 disabling the driver and still be able to listen  for a reply on the PC
port.

 Thanks in anticipation

 Pat Hanson >>
Hello Pat,
Most RS232 - RS485 converters use the RTS line as a read/write line.  You
have to drive the RTS line just before writing to the bus.
BlackBox and Inmac have RS485 conversion stuff.  They range from $99 to
several hundred.  The $99 converter needs the RTS line to control direction,
 the more expensive version has a micro that takes care of that.  I made my
own with a MAX233, a MAX487 and a PIC.
Omega also carries them

Dave Duley