Connect Tech Blue Heat/Net User’s Manual
Revision 0.13
109
Multi-drop 4-wire, full duplex RS-485 communications:
In a multi-drop 4-wire RS-485 network, 2 to 32 devices are connected together. Note that each
RS-485 receiver counts as a device or “load”. In this multi-drop mode of communication, a
master slave protocol must be enforced, that is, all communication is initiated by the master, in
this case a Blue Heat/Net. The communication is “full duplex”, meaning that receive and
transmit traffic occur on different pairs of wires. The Blue Heat/Net can receive and transmit
data from/to a device at the same time.
Basic 2 wire, half duplex multi-drop connection:
In a 2-wire RS-485 network, 2 to 32 devices are connected together. Note that each RS-485
receiver counts as a device or “load”. In this multi-drop mode of communication a master slave
protocol must be enforced, that is, all communication is initiated by the master, in this case a
Blue Heat/Net. The communication is “half duplex”, meaning that receive and transmit traffic
occur on the same wire. The Blue Heat/Net and devices can not receive data and transmit data at
the same time.
Note that the Re/- and the Trans/- signals are connected together. This is
performed at the DB-9 connectors. All communication between devices occurs over a single pair
of wires; this can lower the cost of wiring your RS-485 network.