The table below shows the factory default jumper settings for the
Model 1000RCM703120 DB25/RJ-45 rear card. Following the table is
a description of each jumper’s function and possible settings. When
configuring the jumpers, take care not to lose the individual straps.
LK1: (Receive Pair) Pin 2-to-Ground Connection
This setting determines whether or not pin 2 of the receive pair is
sent to earth ground. This connection should not be made in most
cases.
LK1
Setting
Strap On
Pin 2-to-GND Connection Made
Strap Off
Pin 2-to-GND Connection Broken
LK2: Receive Shield (Pin 3)-to-Ground Connection
This setting determines whether or not the RX shield (pin 3) is
connected to earth ground. This connection may help EMC perform-
ance in some cases.
LK2
Setting
Strap On
Pin 3-to-GND Connection Made
Strap Off
Pin 3-to-GND Connection Broken
LK3: (Transmit Pair) Pin 4-to-Ground Connection
This setting determines whether or not pin 4 of the transmit pair is
sent to earth ground. This connection should not be made in most
cases.
LK3
Setting
Strap On
Pin 4-to-GND Connection Made
Strap Off
Pin 4-to-GND Connection Broken
9
120 OHM REAR CARD JUMPERS
Jumper
Function
Factory Default
LK1
RX Pin 2 to GND
Strap Off
LK2
RX Shield (Pin 3) to GND
Strap Off
LK3
TX Pin 4 to GND
Strap Off
LK4
Clock Synchronization
Strap Off
LK5
(DTE) SGND to FGND
Strap On
LK4: Clock Synchronization (EIA-530/V.35 vs. X.21)
This setting determines whether clocks are common or separate.
Separate (non-synchronized) clocks are used for the EIA-530/V.35 ter-
minal interface. Common (synchronized) clocks are used for the X.21
terminal interface. If clocks are synchronized, a DB-25 to DB-15
adapter cable should be used between the Model 2703RC-A and the
X.21 terminal device (see Appendix B and Appendix C for details).
LK4
Setting
Strap On
Clocks Synchronized (X.21)
Strap Off
Clocks not Synchronized (EIA-530 and V.35)
LK5: DTE Signal Ground-to-Frame Ground (with Resistor)
This setting determines whether or not the DTE signal ground
(DB-25 pin 7) is connected to frame ground (pin 1) by way of a 100
ohm resistor. This connection is recommended in the EIA-530 specifi-
cation as a current limiter for ground fault events.
LK5
Setting
Strap On
SGND-to-FGND Connection Made
Strap Off
SGND-to-FGND Connection Broken
3.2.2 CONFIGURING THE MODEL 1000RCM70375 REAR CARD
The Model 1000RCM70375 DB15/Coax Ohm rear card has two
configuration jumpers (LK1 & LK2). Figure 5 (below) shows the loca-
tions of the jumpers on the 75 Ohm rear card.
10
Figure 5. Jumper Locations for the Model 1000RCM70375 Rear Card
LK1
LK2
