Oc-3 / Stm-1 (Optical / Coaxial) 155.52 Mbps Interface; Oc-3 / Stm-1 Interface Transmit Clocking; Oc-3 / Stm-1 Interface Receive Clocking; Figure 8-3. Cdi-50 Oc-3 / Stm-1 Interface - Comtech EF Data CDM-700 Installation And Operation Manual

CDM-700 High Speed Satellite Modem
Clock Modes
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.
Single Mode
Or
Multi-Mode
Interface
Coaxial
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)
Tx-Terr
Internal
J1
Rx
SC
SC
Optical
Optical
Transceiver
Transceiver
Tx
Loopback
J3
Tx
STS-1
STS-1
Transceiver
Transceiver
Rx
J2

Figure 8-3. CDI-50 OC-3 / STM-1 Interface

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.
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.
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.
Processor
Processor
Clk
Mux /
Mux /
&
Demux
Demux
Data
PLLs
PLLs
μC
Rx
Rx
Buffers
Buffers
Interface
Interface
Loopback
Loopback
OC-3 / STM-1 Card
8–4
Revision 5
MN/CDM700.IOM
Modem
Interface