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Once you have properly set the configuration switches, you are
ready to connect the Model 285 to your system. This section tells you
how to properly connect the Model 285 to the RS-485 and RS-232
interfaces, and how to operate the Model 285.
4.1 CONNECTION TO THE RS-485 INTERFACE
To function properly, the Model 285 must have one or two twisted
pairs of metallic wire. These pairs must be "dry" (unconditioned)
metallic wire, between 19 and 26 AWG (the higher number gauges
may limit distance somewhat).
For your convenience, the Model 285 is available with several dif-
ferent physical interfaces on the RS-485 side: DB-25 (following the
RS-520 standard), RJ-11 jack, RJ-45 jack, and terminal blocks with
strain relief.
4.1.1 4-WIRE CONNECTION USING THE DB-25
The DB-25 connector on the Model 285's RS-485 side conforms to
the RS-530 interface standard. When connecting to an RS-485
device that also conforms to the RS-530 standard, your cable should
be "crossed over" in the manner shown below:
MODEL 285
SIGNAL
DB-25 PIN
XMT+
2 ...........................3
XMT-
14 ...........................16
RCV+
3 ...........................2
RCV-
16 ...........................14
NOTE: It is not necessary that the RS-485 device adhere to the RS-530 stan-
dard. However, you must make sure that the signals, polarities, and pairing of
your connection conform to the above diagram.
RS-485 (530) DEVICE
DB-25 PIN
SIGNAL
RCV+
RCV-
XMT+
XMT-
7
4.1.2 4-WIRE CONNECTION USING RJ-11 OR RJ-45
The RJ-11 and RJ-45 connectors on the Model 285's RS-485 side
are pre-wired for a standard TELCO wiring environment. The
signal/pin relationships are shown below:
RJ-11
SIGNAL
1...................GND*
2...................RCV-
3...................XMT+
4...................XMT-
5...................RCV+
6...................GND
In most modular RS-485 applications it is necessary to use a
"cross over" cable. The diagram below shows how a cross over cable
should be constructed for an environment where both the Model 285
and the RS-485 device use a 6-wire RJ-11 connector. Similar logic
should be followed when using RJ-45 connectors or a combination of
the two.
MODEL 285
SIGNAL
PIN#
GND*
1
RCV-
2
.........................4
XMT+
3
.........................5
XMT-
4
.........................2
RCV+
5
.........................3
GND
6
*Connection to ground is optional
1
2
3
4
5
6
**Standard AT&T pin assignements - yours may be different.
RJ-45
SIGNAL
1 .................N/C
2 .................GND*
3 .................RCV-
4 .................XMT+
5 .................XMT-
6 .................RCV+
7 .................GND
8 .................N/C
RS-485 DEVICE
PIN#
422 SIGNAL
XMT-
RCV+
RCV-
XMT+
1
2
3
4
5
6
7
8
8
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