Comtech EF Data CDM-700 - Manual (Page 136)

CDM-700 High Speed Satellite Modem Revision 5
Clock Modes MN/CDM700.IOM
8.3 CDI-50 OC-3 / STM-1 (Optical / Coaxial) 155.52 Mbps Interface
The CDI-50 OC-3 / STM-1 interface has one optical port and one coaxial (copper) port. Only one
of the ports is active at a time, and the selected port operates at 155.52 Mbps. Figure 8-3 shows
the interface.
Figure 8-3. CDI-50 OC-3 / STM-1 Interface
8.3.1 CDI-50 OC-3 / STM-1 Interface Transmit Clocking
The only clock source for the interface is derived from the Tx data signal applied to the module
input. Internal Clock and Rx Loop-Timed operation do not apply to this interface.
8.3.2 CDI-50 OC-3 / STM-1 Interface Receive Clocking
When the Rx Buffer is disabled, the receive clock is the Rx-Sat. In this mode, make sure the Rx
Buffer is set to minimum to reduce latency.
When the Rx Buffer is enabled, the Rx clock selections are as follows:
Rx-Sat (default)
Selecting this clock disables the Rx Buffer because the input and
output clocks are both Rx-Sat. Normally, the Rx Buffer is set for
minimum when Rx-Sat is selected.
Tx-Terr
Uses the clock from the Tx input to clock out the Rx Buffer. The Tx and
Rx data rates are the same on this interface, so asymmetric clocking
where Tx
≠ Rx is disallowed.
Internal
The Internal Clock comes from the modem. It is derived from either
the Ext Ref (J7) or Int Ref oscillator in the main part of the modem –
not from the data interface.
SC
Optical
Transceiver
SC
Optical
Transceiver
Modem
Interface
Clk
&
Data
μC
OC-3 / STM-1 Card
STS-1
Transceiver
STS-1
Transceiver
Single Mode
Or
Multi-Mode
Interface
Processor
Mux /
Demux
PLLs
Rx
Buffers
Interface
Loopback
Processor
Mux /
Demux
PLLs
Rx
Buffers
Interface
Loopback
Loopback
J2
Coaxial
Interface
Tx
Rx
Rx
Tx
J3
J1
8–4