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Q: How Do I Connect Two RS-422 Devices Together?
A1: The connections
for two devices with Receive and Transmit RS-422 signals is
shown in Figure 1. This represents the RS-422 connections
of a device, card or converter. This is a "4-wire" connection,
one pair of twisted wires is used for Receive, the other for
Transmit. Signal Ground is used as a Common reference.
Figure 1 applies to many Ethernet/Serial
Servers and a few B&B RS-485 Converters such as the 485SD9TB,
485LPRJ, 485SD9R, 485SD9RJ.
A2: There are
many conditions that use a "2-wire" RS-422, where a signal
master uses one wire pair and ground to talk to multiple devices
that receive only (no Transmit). RS-422 is used to go the
distance and to multi-drop to connect multiple listeners.
This connection is commonly used for Security/Surveillance
Video Cameras to control the Pan/Tilt/Zoom (available from
Pelco or others), or to connect displays for signage indoors
or outdoors, clock displays, etc. Depending on the device
receiver type, up to 32 (12K impedance nodes) or 11 RS-422
receivers can be connected without a repeater.
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