Contemporary Control Systems AI-SRVR Servers to Ethernet Installation Guide - Manual (Page 10)

TD000200-0IH
10
485X — AC-Coupled EIA-485
The AC-coupled EIA-485 transceiver offers advantages over the DC-
coupled version. No bias adjustments are needed and wiring polarity is
unimportant. Much higher common mode voltage levels can be achieved
with AC coupling because the transformer coupling has a breakdown
rating of 1000 Vdc.
However, AC-coupling also has disadvantages. AC-coupled segments
are shorter (700 feet max) and are limited to 13 nodes compared to the 17
of DC-coupling. AC-coupled transceivers operate only at 1.25, 2.5 and
5.0 Mbps while DC-coupled transceivers function over all six standard
data rates.
Cabling rules for 485X are similar to those for 485. Wire nodes in a
daisy-chain fashion. On the end devices, insert a jumper at E1 on both
485X daughter boards to invoke 120 ohms of termination or leave the
jumpers open and install a 120-ohm, ¼ watt resistor across pins A and B
of the screw terminals at each end of the bus segment. Refer to page 3
for connector wiring. Termination should not be applied to any device
located between the two ends of the segment. Do not mix 485 and 485X
devices on the same segment; however, bridging the technologies is
possible with active hubs having appropriate transceivers. To extend
485X segments, use a hub as discussed under the 485 section. Make sure
the active hub transceivers are 485X types. Cable inversion is insignificant.
ELECTROmAGNETIC COmpATIBILITy
AI-SRVR units comply with Class A radiated and conducted emissions as
defined by CFR 47, Part 15 and by EN55022. This equipment is intended
for use in nonresidential areas.
warning
This is a Class A product as defined in EN55022. In a domestic environment
this product may cause radio interference — in which case the user may be
required to take adequate measures.