SATELLINE-EASy / SATELLINE-EASy 869
User Guide, Version 3.0
79
15.2.4
RS-485 wiring
Both ends of the transmission line should be terminated by connecting a separate terminating
resistor between the positive and negative signal wire. Typical values range from 100 – 120
ohm depending on the characteristic impedance of the line.
FUSE = 1 A slow (+6 … +30 V assembly) or 2.5 A slow (+3 … +9 V assembly)
NOTE! The RS-485/422 standards define only the electrical parameters of the signals (signal
level etc.). The connectors and the names of the signals are NOT defined. Different RS-485/422
standards or proprietary buses specify different names for the wires. Common signal names used
are ‘A’ and ‘B’, ‘+’ and ‘-’ or ‘hot’ and ‘cold’. Unfortunately these names define the polarity of
the signals only for a specific system or specific equipment. In reality ‘A’ of one system can
actually be ‘B’ of another. If the polarity is wrong, the data will be inverted. Usually the simplest
way to solve the issue is the trial and error method, as RS-485 signals can be connected only
two ways.
