User Manual

RS-485 Network
E-
2 ADAM 4000 Series User’s Manual
EIA RS- 485 is indu stry’s most w idely used bidirectional, balanced
transmission l ine st andard. It i s specifically de veloped for i ndustrial
multi-drop syste ms th at sh ould be able to transmit and receive d ata at
high rates or over long distances.
The specifications of the EIA RS-485 protocol are as follows:
-Max line length per segment: 1200 meters (4000 feet)
-Throughput of 10 Mbaud and beyond
-Differential transmission (balanced lines) with high resistance against
noise
-Maximum 32 nodes per segment
-Bi-directional master-slave communication over a single set of twisted
pair cables
-Parallel connected nodes, true multi-drop
ADAM modules are fully i solated and use just a si ngle set of twisted
pair wi res to send and receive! Since the nodes are c onnected i n
parallel they can be freely disconnected from the host without affecting
the fun ctioning of th e remaining nod es. In indu stry sh ielded t wisted
pair is preferable due to the high noise ratio of the environment.
When nodes c ommunicate t hrough t he network, n o se nding c onflicts
can occur since a simple command/response sequence is used. There is
always one initiator (with n o address) and many slaves (with address).
In this case the master is a personal computer that is connected with its
serial, RS-232, port to an ADAM RS-232/RS-485 converter. The slaves
are the ADAM I/O modules. When modules are not transmitting data,
they are i n listen m ode. The host co mputer in itiates a
command/response seq uence wi th o ne of t he m odules. C ommands
normally cont ain t he ad dress o f t he m odule t he host wa nts t o
communicate with. T he module with the matching a ddress carries out
the command and sends its response to the host.