Plesiochronous Buffer; Remote Interface Specification - Comtech EF Data SDM-650B Installation And Operation Manual

Configuration

3.2.5.5 Plesiochronous Buffer

User data from the DEMUX section is fed into a plesiochronous buffer. The buffer size is
user selectable in 16-bit increments, from 384 to 262144 bits. The buffer is automatically
centered on resumption of service after an outage, or may be commanded to center in the
interface configuration section (from the front panel or remotely). For obvious reasons,
manual centering will generally not be plesiochronous.
The fill status is available as a monitor function and is accurate to 1%. Overflow or
underflow incidents will be momentarily indicated by red LEDs on the module. They are
stored in the Stored Faults (StFaults) section of the M&C status registers, along with the
date and time of the incident, provided by the modem internal clock. They are stored in
battery-backed RAM.
The user may select to have the data clocked out of the buffer from four clock sources:
•
•
•
•
Satellite clock selection is similar to buffer bypass. Problems on either the TX terrestrial
clock or the external clock (if selected) will substitute satellite clock, and a fault will be
signaled.

3.2.5.6 Remote Interface Specification

Refer to Appendix B, Section B.2, for the remote interface specifications for the
asynchronous overhead channel unit.
3–36
Recovered EXT clock from user terrestrial input data
User-supplied EXT-REF reference clock
Satellite clock which is phase-locked to the demultiplexer
Internal clock source
SDM-650B Satellite Modem
Rev. 5