Contemporary Control Systems EXP Expansion Modules User Manual - Manual (Page 19)

AC coupling due to the transformer coupling which has a 1000
Vdc breakdown rating.
There are disadvantages to the AC-coupled transceiver as
compared to the DC-coupled technology. The DC-coupled
distances are longer (900 feet) compared to the AC-coupled
distance (700 feet).
The cabling rules of the -485X are similar to the -485. Wire a
maximum of 13 NIMs (reduce by one for each hub port) in a
daisy-chain fashion leaving the end devices as either NIMs or
hub ports. On these NIMs or hub ports insert a jumper at E1 on
both -485X daughterboards to invoke 120-ohm termination
resistors or leave the jumpers open and insert RJ-11 style
passive terminators. In the case of a hub port, an RJ-11 style tap
is required. Termination should not be applied to any of the
NIMs located between the two end NIMs or hub ports of the
segment. Do not mix -485 (-485D) and -485X NIMs together
on one segment; however, bridging of the technologies is
possible using two appropriate expansion ports on the MOD
HUB. To extend -485X segments, use a hub as discussed under
the -485 section. Cable inversion is not of any consequence.
Figure 2-3. AC Coupled EIA-485 Option (-485X)
TD401600-0M
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