Connect Tech Blue Heat/Net User’s Manual
108 Revision
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Any noise injected into the wires is cancelled at the receiver, leaving only the original,
undistorted data signal. Twisted pair cables are always used in RS-485, this ensures that the
communications are robust and as error free as possible. RS-485 signal levels are between 0 and
5 Volts, the differential voltage can be as little as 200mV.
RS-485 can operate in three different modes: a 4-wire full duplex interface, 4-wire multi-drop
full duplex interface and a 2-wire half duplex interface. A full duplex (bi-directional) RS-485
communications interface requires at least four wires, two for transmit and two for receive. A
half duplex interface only requires two wires, this provides a cost effective cabling solution.
Multi-drop is a great feature of RS-485. Multiple RS-485 devices can be bussed together in a
daisy chain type fashion to create a network. Up to 32 devices may be connected together on the
same network. In multi-drop networks, one of the devices (usually the computer) is designated
as the master, and all the other devices are designated as slaves. All communication is initiated
by the master. The master and slave designations are established by your communications
application.
Basic 4-wire, full duplex RS-485 communications:
In a 4-wire RS-485 network, two devices are connected together, for example your Blue
Heat/Net RS-485 port and an RS-485 device.
