SLM-3650 Satellite Modem
Revision 3
Operation
MN/SLM3650.IOM
3–87
3.6
Clocking Options
Clocking of the data from the terrestrial equipment to the satellite (and vice versa) will
depend on the application. This section describes the most common options and
recommended configurations.
3.6.1
EIA-232, EIA-422, or V.35 Master/Master
Refer to Figure 3-27 for:
•
Clocking block diagram
•
Transmit clock options
•
Buffer clock options
•
V.35 timing signals
•
EIA-422 timing signals
3.6.2
EIA-232, EIA-422, or V.35 Master/Slave
Refer to Figure 3-28 for:
•
Clocking block diagram
•
Transmit clock options
•
Buffer clock options
•
V.35 timing signals
•
EIA-422 timing signals
The use of loop timing in the modem is an option for both EIA-422 and V.35 operation.
SCT (LOOP): SCT (INTERNAL) clock no longer applies when the modem has loop
timing on. The TX clock source is now recovered from the RX satellite data. This
recovered clock is put out on the ST line and is used to clock the terrestrial equipment.
The transmit terrestrial clock is now essentially the same as the RX satellite clock, except
that it has been buffered by the terrestrial equipment. Select TX TERRESTRIAL for the
TX clock source when in loop timing, if the user equipment is being slaved off of the
modem. The SCT (LOOP) indication serves as a reminder that the SCT internal clock is
now the recovered clock, not the internal oscillator. Select SCT (LOOP) when the
terrestrial equipment does not provide a transmit terrestrial clock.
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