User Manual

54 ADAM-4572 User's Manual
EIA RS-485 is the industry’s most widely used bidirectional, balanced
transmission line standard. It is specifically developed for industrial multi-
drop systems that should be able to transmit and receive data at high
rates or over long distances.
The specifications of the EIA RS-485 protocol are as follows:
• Maximum line length per segment: 1200 meters (4000 feet)
• Throughput of 10 Mbaud and beyond -Differential transmission (bal-
anced lines) with high resistance against noise
• Maximum 32 nodes per segment
• Bi-directional master-slave communication over a single set of twist-
ed-pair cables
• Parallel connected nodes, true multi-drop
ADAM-5000 systems are fully isolated and use just a single set of twist-
ed pair wires to send and receive! Since the nodes are connected in
parallel they can be freely disconnected from the host without affecting
the functioning of the remaining nodes. An industry standard, shielded
twisted pair is preferable because of the high noise ratio of the environ-
ment.
When nodes communicate through the network, no sending conflicts
can occur since a simple command/response sequence is used. There is
always one initiator (with no address) and many slaves (with addresses).
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-5000 systems. When systems are not transmitting data,
they are in listen mode. The host computer initiates a command/response
sequence with one of the systems. Commands normally contain the ad-
dress of the module the host wants to communicate with. The system
with the matching address carries out the command and sends its re-
sponse to the host.