Wiring Instructions
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netTAP NT 50 | Gateway Devices
DOC091202UM09EN | Revision 9 | English | 2013-02 | Released | Public
© Hilscher, 2010-2013
10.8 RS-422
Device Damage!
!
Make sure that the NT 50 device and the remote device via RS-422
have the same potential or insert a galvanic isolation, to avoid compen-
sation current between the used devices.
The lines of this industry bus interface are operated in push-pull action, four
lines are required which can be controlled in half duplex or full duplex
mode. This interface has been designed for one master and at maximum
10 slaves. Using repeaters, using even more slaves is possible.
Cable lengths of up to 1.2 km (at low baud rates) and data transmission ra-
tes of up to 10 MBit/s (at maximally 12 m length of line) are possible. The
maximum useable transmission rate depends on the technical data of the
used devices.
The following illustration shows wiring for RS-422:
Figure 17: RS-422 Wiring
Bus Requirements:
The bus cable must be a shielded 4.wire twisted pair cable. Each pair of wi-
res has to be used for exactly one data transmission direction. The shield
should be connected at both ends to the potential equalization system.
On each end, the bus requires a termination resistor (LT) of 90
Ω
to 150
Ω
between the lines. This value depends on the characteristic wave imped-
ance of the cable.
The pull-up and pull-down resistors should have a resistance of 390
Ω
up to
650
Ω
.
