Mocomtech CDM-570 - Manual (Page 215)

CDM-570/570L Satellite Modem with Optional IP Module Revision 4
Clocking Modes MN/CDM570L.IOM
9.2 Receive Clocking
There are three receive clocking modes in the CDM-570L, plus an additional setting used
for Drop and Insert only – see later section.
9.2.1 Buffer Disabled (Rx Satellite)
When the buffer is disabled, the receive clock (Receive Timing, or RT) is derived directly
from the demodulator, and hence will be subject to plesiochronous and Doppler offsets.
In certain instances, this may be acceptable. There is still a minimum buffer in use to de-
jitter the effects of removing overhead framing.
G.703: Applicable.
9.2.2 Buffer Enabled, Tx=Rx
In this instance, it is required that the buffer be enabled, so that the clock and data
appearing on Receive Timing and Receive Data (RT and RD respectively) are
synchronous with the transmit clock. This is a relatively simple case, as the output clock
for the buffer is derived directly from either ST, TT or the external source.
G.703: Applicable.
9.2.3 Buffer Enabled, Rx<>Tx
This is an uncommon case, where the receive data rate does not equal the transmit clock.
The modem will generate a phase-locked buffer output clock which uses the selected
reference, regardless of its frequency in relation to the receive data rate.
G.703: Applicable.
9.3 X.21 Notes
For X.21 operation, use the RS-422 pins, but ignore Receive Clock if the Modem is DTE,
and ignore Transmit clocks if the Modem is DCE.
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