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CHAPTER 3: Installation
Point-to-Point
When only two devices are connected to the line in a point-to-point application,
each device should have the termination network connected to the line. Set switch
S2 to the “TERM” position.
Multipoint
For multipoint applications, switch S2 should be in the “UNTERM” position on all
the RS-232↔485/422 Converter devices in the network except for the two units at
the extreme opposite locations on the line. The extreme opposite devices are the
two devices that have the greatest cable length between them, which may not
necessarily be the devices that are physically located the farthest apart. These two
units should be set in the “TERM” position (see Figures 5 and 6). If any of the
other RS-232↔485/ 422 Converters were configured as “terminated,” the amount
of distortion could increase—possibly causing errors in the data being transmitted.
3.1.8 N
ORMAL
/L
OOPBACK
O
PERATION
The Normal/Loopback switch (S1) is a two-position pushbutton switch extending
through the front panel. The Normal position permits normal operation of the
RS-232↔485/422 Converter. The Loopback position allows data coming into the
RS-232↔485/422 Converter to be sent back out the same port. This is for testing
the connection between the RS-232↔485/422 Converter and the device attached
to each port.
Normal
When this switch is in the normal mode, data is passed through the Converter
from the RS-232 port to the RS-485 port and vice versa.
Loopback
When set to the loopback mode, any data received at the RS-485 port will be
transmitted back out the RS-485 port and any data received at the RS-232 port will
be transmitted back out the RS-232 port.
3.1.9 RS-485 I
NTERFACE
L
INE
B
IASED
(F
AIL
-S
AFE
)
If S3 is in the Off position, there is no line bias. If S3 is in the On position, there is
line bias.