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When the cable is thin or EMI is strong or the there are too many other devices, the
transmission distance will be shorten.
3. Connection and terminal resistance
When arranging the wires, the way of connection use the way of snakelike, both of the ends
must connect 120Ω terminal resistance, the simple connection is as the Chart 7, the distance is no
longer than 7 meters.
120Ω
1#
D
120Ω
Controller
4. Problems in the practical application
In the practical application, most of the clients use the star like connection mode, in this case,
the terminal resistance must connect the two devices which at the longest distance, such as 1＃
and 15＃, as this kind of connection doesn't meet the requirement of RS485's industry standard,
so it will cause the problems of signal reflex, the ability of anti-interference reduces, the reliability
of signal control reduces. In this case, the RS485 divider is recommended, it can change the star
like connection to the connection which can meet RS485's industry standard, so that it can
improve the reliability of communication.
2#
3#
Picture 2
A+
B-
A+
B-
1#
Picture 3
4#
2#
3#
40
. . . . .
120Ω
32#
. . . . .
. . . . .
120Ω
31#
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