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CHAPTER 3: Configuration
3.1.3 N
ODE
T
ERMINATION
(S
WITCH
7)
You can select whether or not the termination network for the receiver is
connected to the line. Terminating the devices on the extreme ends of the line
reduces distortion and improves overall signal quality in most applications. The
factory setting is with Switch 7 in the TERM position.
In point-to-point applications, both devices should have the node termination
option enabled.
In multipoint applications, only the two devices at the extreme ends of the line
should be terminated. Configuring any of the other devices on the line for node
termination would result in an increase in the amount of distortion and possible
data errors.
3.2 Jumpers
Four options are user-configurable via internal jumpers:
• Constant Carrier/Switched Mode - Jumper W2
• RTS/CTS Delay (for Switched Mode) - Jumper W2
• Full/Half Duplex - Jumper W3
• Frame Ground/Signal Ground - Jumper W1
3.2.1 C
ONSTANT
C
ARRIER OR
S
WITCHED
M
ODE
Jumper W2 is used to select Constant Carrier or Switched Mode. This option
determines the use of the Request To Send signal, with selection dependent on
your particular application. When the jumper block is in the Constant Carrier
position, Constant Carrier Mode is selected. If Switched Mode is desired, the
jumper block would be placed in one of the four RTS/CTS delay positions. See
Figure 4-1 for the jumper’s location on the printed circuit board. Each mode is
discussed below.
In Constant Carrier Mode, the unit functions as if RTS is constantly asserted. The
EIA 485 transmitter is always on, and the unit CTS signal remains high. Any data
sent by the attached RS-232 device is automatically transmitted by the Line Driver.
The RTS LED on the unit’s front panel will always be on, and the CD indicator of
the remote Line Driver(s) will remain lit. Constant Carrier Mode is most
commonly used in multipoint applications that have a “master” device
communicating with two or more “slaves.” The master DTE is configured for
Constant Carrier Mode, while the slave devices are set to Switched Mode.
