3.1.2 Switch S1
The chart below shows the default configurations for Switch S1. A
description of all S1 options follows this table.
Switch S1-1: RDL Type
Switch S1-1 selects the type of Remote Digital Loopback that the
2720 will initiate when the RDL is initiated from this unit. The 2720 will
respond to both the V54 and the CSU loopback regardless of the set-
ting of S1-1
S1-1
RDL Type
On
Initiate a V.54 RDL loop when selected
Off
Initiate a CSU loopback when selected
Switch S1-2: Tx Clock Select
Switch S1-2 selects the clock that is used to accept the Transmit
Data from the DTE interface. Standard DTE interfaces will transmit
data with respect to the External Clock. In some cases a DTE interface
will transmit with respect to the Transmit clock sent out from the 2720.
Please review the information provided with your DTE equipment for
more information on its' operation. In most cases when there are errors
on the line only in the direction of the transmit data either S1-2 or S1-3
can be changed to solve the problem.
S1-2
Tx Clock Select
On
Transmit data accept with respect to the transmit
clock from the 2720
Off
Transmit data accept with respect to the external
clock from the DTE
Switch S2-6 and S2-7: Clock Mode
Set Switch S2-6 and S2-7 to determine the 2720’s transmitter tim-
ing.
S2-6
S2-7
Clock Mode
Off
Off
Network Clock. Transmitter timing is
derived from the received line signal.
On
Off
Internal Clock. Transmitter clock is
derived from an internal oscillator.
Off
On
External Clock. Transmitter clock is
derived from DTE interface.
NOTE 1: When using the Model 2720 as a high-speed short
range modem, one unit of the link must be configured in
Internal/External Clock mode, and the opposite end unit must be
configured for Network Clock mode.
If the ERR LED on the front of the unit is flashing (or on) it could
be an indication of a clocking problem. Double check your clock
mode settings and your Tx Clock Select (S1-2) and Tx Clock
Invert S1-3 settings.
Switch S2-8 Reserved
9
10
S1 SUMMARY TABE
Position
Function
Factory Default
Selected Option
S1-1
RDL Type
On
S1-2
Tx Clock Select
Off
S1-3
Tx Clock Invert
Off
S1-4
Line Build Out
Off
S1-5
Off
S1-6
Reserved
Off
S1-7
Reserved
Off
S1-8 Reserved
Off
V.54 RDL
External Clock
Normal
0dB
