Hi..


I Donnow What u c in your circuit, but by what I See
from datasheet, is that the MAX485 Designed to half duplex
communication, so I Suppose they use somekind combination with 2 of them for full duplex. (txd,rxd)
duplex.
see http://www.maxim-ic.com/
/quick_view2.cfm/qv_pk/1111/ln/en

I'm not really know alot about communication ...
I Hope I'm helping.
Goodluck
OK