Contemporary Control Systems USB222 Adapters - Manual (Page 5)

TD040900-0II
5
-TB5 Twisted-pair Bus
The -TB5 transceiver accommodates twisted-pair cabling via a pair of
RJ-45 jacks which allow the unit to be daisy-chained at any location on
the bus segment Usually IBM type 3 unshielded twisted-pair cable
(UTP) is used, but shielded cable (STP) can also be used to provide
continuous shielding between devices.
When the USB22-TB5 is located at the end of a bus segment, Apply the
provided 100-ohm terminator to the empty RJ-45 jack to match the cable
impedance.
-485 DC-Coupled EIA-485
Two models support DC-coupled EIA-485 segments. The USB22-485
provides dual RJ-45 jacks and the USB22-485/S3 offers a 3-pin screw
terminal. Each segment can be up to 900 feet of IBM type 3 (or better)
STP or UTP cable while supporting up to 17 nodes. Make sure the phase
integrity of the wiring remains consistent throughout the network. All
phase A signals on NIMs and hubs must connect together. The same
applies to phase B. Refer toFigure 1 Figures 1 and 2 for connector
wiring.
Termination
If the NIM is located at the end of a segment, apply 100 ohms of
termination. For the USB22-485, insert a terminator in its empty RJ-45
jack. For the USB22-485/S3, attach a resistor to its 3-pin connector.
Bias
Bias must also be applied to the network to prevent the differential
receivers from assuming invalid logic states when the signal line is
floated. Bias is provided on the USB22-485 by a set of 806-ohm pull-up
and pull-down resistors.
Ground
All devices on the segment should be referenced to the same ground
potential to achieve the common mode voltage (+/–7 Vdc) required for
the EIA-485 specification. A ground connection is not provided by the
NIM. It is assumed adequate grounding is supplied by the existing
equipment. Refer to the existing equipment user manual for a discussion of
grounding requirements.