ZyWAN User Manual
Getting started with your ZyWAN
© 2008 Arcom Issue D
20
RS-485 / RS-422 wiring diagrams
When connecting RS-485 or RS-422 devices in a multidrop configuration, there must
usually be a 120
Ω
termination resistor at one or both end devices in the network, but
NOT on any devices in the middle of the loop. The ZyWAN provides a 4-wire RS-
485/422 interface.
In RS-485 or RS-422 systems, the ground connection is optional. It is typically used to
connect the cable shield for a shielded, twisted pair cable. In the ZyWAN, the RS-
485/422 ground is common with the RS-232 grounds, but is isolated from the metal
case. In order to avoid ground loops, connect the cable shield to the RS-485/422 GND
AT ONLY ONE POINT in the network.
The correct device connection arrangements are shown in the following wiring
diagrams:
1st Device
Middle
Device(s)
End Device
TX+
TX-
GND
TX+
TX-
TX+
TX-
2-wire RS-485 Device Connections
End devices usually need 120 ohm termination resistor,
optional middle device(s) must not have resistor.
Master Device
Middle
Device(s)
End Device
TX+
TX-
RX+
RX-
GND
RX+
RX-
TX+
TX-
4-wire RS-485/422 Device Connections
End device (and RS-485 Master) may need 120 ohm termination
resistor, optional middle device(s) must not have resistor.
Drawing is labeled as if devices are DTE. Direction of arrows is
correct, regardless of RX/TX labeling on a given device.
RX+
RX-
TX+
TX-
Drg. S15037-02
(Optional)
(Optional)
Summary of Contents for ZyWAN
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