S1-2 and S1-3: Rate Adaptation
Switches S1-2 and S1-3 are set in combination to allow the Model
2703-X21 to adapt to terminal devices running at data rates of less than
2.048 Mbps (The network rate remains 2.048 Mbps regardless of the
terminal rate adaptation setting). The setting you select should match
the data rate of your terminal device.
S1-2
S1-3
Setting
Off
Off
2.048 Mbps
On
Off
1.024 Mbps
Off On
512
kbps
On
On
256 kbps
S1-4: Loopback Test Enable
Depending upon the setting of switch S1-4 the Model 2703-X21 will
either be continually in loopback mode, or loopback mode will be
enabled by pressing and holding the front panel switch. Since the
front panel switch is spring loaded–it returns to “Normal” operation
when pressure is released–this DIP switch provides a way of leaving
the Model 2703-X21 in “unattended” loopback mode for remote test
purposes.
S1-4
Setting
On
Continual “unattended” loopback mode
Off
Loopback activation by front panel switch
S1-5: Data Inversion
The setting for switch S1-5 determines whether or not the data
stream from the local DTE is inverted within the Model 2703-X21 before
being passed to the G.703 network. The ability to invert the data
stream may be necessary when the Model 2703-X21 is being used with
an embedded G.703 device that inverts the data on the remote end.
Normally, data inversion is not necessary.
S1-5
Setting
On
Data inverted
Off
Data not inverted
S1-6, S1-7 & S1-8 Not Used
5
3.2 INTERNAL JUMPER SETTINGS
The Model 2703-X21’s seven jumpers are located on the PC board
inside the unit. To access the jumpers, follow these instructions:
1.
Insert a flat head screw driver into an open slot on either side
of the case, as in Figure 3. Twist the screw driver head slightly
and the top half of the case will separate from the lower half,
as in Figure 4, below.
2.
Remove the Network Interface Module by lifting gently upward
on it until it comes free from the Model 2703-X21 main PC
board.
3. Slide out the Network Interface Module and locate the jumpers
on the bottom side of the board.
4.
Configure the jumpers according to the section below and
return the Network Interface Module and cover to their proper
positions.
The internal jumpers mounted on the Model 2703-X21’s PC board
(labeled LK1 - LK7) are used to configure the 75 ohm or 120 ohm
network link parameters. Figure 5 (below) shows the location of the
Model 2703’s jumpers on the internal PC board.
6
Figure 3. Opening the 2703 Case with a Small Screwdriver
Figure 4. Opening the 2703 Case With a Small Screwdriver
NOTE: Revision B Firmware (or newer, Implemented 6/19/98)
has been adopted to correct signal polarity at 1.024 Mbps, 512
kbps, and 256kbps. To operate Revision B Firmware units with
Revision A (or older) units at one of these sub-rates, you must
invert invert the data (Switch S1-5 On. See Below) (Firmware
revision level is printed on the label on the bottom of the unit).
