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Wire up the System
The system uses an RS-485 bus protocol. For this reason, it’s very important
to avoid making a
“STAR” structure
in the cabling. In large systems it’s also important to terminate the bus in a
proper way. This can be done with an ARJ-03 module (explained further in this manual).
RS-485 is a differential bus structure, so cabling must be twisted pair (pairs of CAT5 are twisted).
Data is the middle pair of the Cat5 cable (blue pair).
ARJ03 module:
This is a compact, cheap module which makes it possible to place more than one paging table on
the bus. The module has a jumper for terminating the bus (120 Ohm resistor).
The middle
connector (marked: “To APM”) is used to connect the paging table. The cable used to
connect the paging table to the middle connector may not exceed 2m. If the cable is
longer then 2m, a “star point” is created, so reflections on the data bus may occur and will
result in signal and performance loss. An exception to this rule can be made when the
paging table is connected at the end of the data bus, in other words: when there is no
cable attached to the “Bus Out ” connector.
The ARJ-03 module can be placed under a desk or in a cableway.
Following figure shows the top of the module:
Chapter
4
