Printed in the Federal Republic of Germany TR-Electronic GmbH 2009, All Rights Reserved
12/13/2018 TR - ECE - BA - DGB - 0070 - 17 Page 85 of 108
5.2 SSI transmission technology (RS422), Cable definition
Danger of damage to subsequent electronics due to overvoltages caused
by a missing ground reference point!
•
If the ground reference point is completely missing, e.g. 0 V of the power
supply not connected,
voltages equal to the supply voltage can occur at
the outputs of this interface.
It must be guaranteed that a ground reference point is present at all
times.
With the RS422 transmission one line-pair is used for the signals Data+ and Data–
and one line-pair for the signals Clock+ and Clock–.
The serial data are transmitted without mass reference as a voltage difference
between two corresponding lines.
The receiver evaluates only the difference between the two lines. Therefore common-
mode interferences on the transmission line do not lead to a corruption of the useful
signal.
By the use of shielded and twisted pair cable with min. 0.25mm
2
, data transmissions
over distances from up to 500 meters with a frequency of 100 kHz can be realized.
Under load RS422 transmitters provide output levels of ±2V between the two outputs.
RS422 receivers still recognize levels of ±200mV as valid signal.
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