S1-4: Echo Mode
The setting for switch S1-4 determines whether the Model 2085
echoes data back to the transmitting device (half-duplex mode only).
S1-4
Setting
On
Echo On
Off
Echo Off
S1-5: Carrier Control Method
The setting for switch S1-5 determines whether the carrier is
“Constantly On” or “Controlled by RTS”. This setting allows for
operation in switched carrier, multipoint and/or hardware handshaking
applications.
S1-5
Setting
On
Controlled by RTS
Off
Constantly On
S1-6: Receive Impedance
The setting for switch S1-6 selects the impedance of the input
receiver. You may select either a “low” impedance of 120 Ohms or a
“high” impedance of 16 kOhms. By selecting the proper impedance for
each drop, there may be up to 50 receivers in one application.
S1-6
Setting
On
Low (120 Ohm)
Off
High (16 kOhm typical)
S1-7 and S1-8: 2-Wire/4-Wire Modes
Switches S1-7 and S1-8 are set together to determine whether the
Model 2085 is in 2-wire or 4-wire operating mode.
Note:
2-wire mode
is half-duplex only.
S1-7
S1-8
Setting
On
On
2-wire mode
Off
Off
4-wire mode
7
4.1.2 4-WIRE CONNECTION USING RJ-11 OR RJ-45
The RJ-11 and RJ-45 connectors on the Model 2085's RS-485 side
are pre-wired for a standard TELCO wiring environment. The signal/pin
relationships are shown below:
RJ-11
SIGNAL
RJ-45
SIGNAL
1...................GND*
1 .................N/C
2...................RCV-
2 .................GND*
3...................XMT+
3 .................RCV-
4...................XMT-
4 .................XMT+
5...................RCV+
5 .................XMT-
6...................GND
6 .................RCV+
7 .................GND
8 .................N/C
*Connection to ground is optional
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 2085 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 2085
RS-485 DEVICE
SIGNAL
PIN#
PIN#
RS-422 SIGNAL
GND
†
1 -------------------N/C
RCV-
2 -------------------4
XMT-
XMT+
3 -------------------5
RCV+
XMT-
4 -------------------2
RCV-
RCV+
5 -------------------3
XMT+
GND
†
6 -------------------N/C
10
1
2
3
4
5
6
7
8
1
2
3
4
5
6
