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Installation / Preparation for commissioning
5.3 SSI, RS422 communication technology
RS422 communication requires one cable pair for the signals Data+ and Data– and
one cable pair for the signals Clock+ and Clock–.
The serial data is transmitted without reference to earth as a voltage difference
between two corresponding cables.
The receiver simply evaluates the difference between two cables, so that common-
mode interference on the transmission line does not corrupt the usable signal.
By using shielded stranded pair cable, data transmission can be realised over
distances of up to 500 metres at a frequency of 100 kHz.
Under load, RS422 transmitters provide output levels of ± 2 V between the two
outputs; the receivers still recognise levels of ± 200 mV as a valid signal.
24
Differential signal (A-B)
Idle signal = 3 V
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