User Manual

Appendix E
Appendix E RS-485 Network E
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E.1 Basic Network Layout
Multi-drop RS-485 implies that there are two main wires in an segment.
The c onnected m odules t ap from t hese t wo l ines with s o cal led drop
cables. T hus all connect ions a re parallel and c onnecting or
disconnecting of a node doesn’t a ffect t he net work as a whole. Since
ADAM m odules use t he R S-485 st andard, an d use a n ASCII-based
commands set , they can connect and communicate with all ASCII-
based computers and terminals. The basic layouts that can be used for
an RS-485 network are:
Daisychain
The last m odule of a segment is a re peater. It is directly connected to
the m ain-wires th ereby end ing th e first se gment and starting t he ne xt
segment. U p t o 32 a ddressable m odules c an be diasychained. T his
limitation is a physical one. When using more modules per segment the
IC d river c urrent ra pidly decreases, causing com munication e rrors.
Totally th e netw ork can ho ld up to 256 addressable mo dules. Th e
limitation for this number is the two number hexadecimal address codes
that know 256 combinations. Th e ADAM converter, ADAM repeaters
and the host c omputer are non addressable units a nd therefore are not
included in these numbers.
Figure E-1 Daisychaining