Mux Operation; Demux Operation; Buffer Operation - Comtech EF Data SNM-1001L Installation And Operation Manual

SNM-1001L Satellite Modem
Automatic Uplink Power Control
10.2.3

MUX Operation

The MUX receives terrestrial and AUPC data from the selected receivers. The terrestrial
data flows into a small First In/First Out (FIFO) buffer. The FIFO buffer aids in the rate
exchange between the terrestrial data rate and the overhead rate. The data can be clocked
into the MUX by the terrestrial clock or an internal clock.
AUPC data is received from a serial M&C interface. The overhead clock is generated
from the terrestrial data clock by a phase-locked loop. Inside the multiplexer, overhead
bits (1/16) are added to create a sub-frame, frame, and multi-frame structure. The AUPC
data from the M&C interface is inserted into the framing structure. The framed data is
output to the modulator card on the modem at the overhead rate.
10.2.4

DEMUX Operation

The DEMUX section functions in a "reverse" manner to the MUX side. Data, including
overhead, is received from the Demod card in the modem at the overhead rate.
The DEMUX locates the framing in the overhead and locks to the frame sync pattern
generated by the multiplexer on the transmitting end. Once locked to the framing, the
terrestrial data is clocked into the Doppler buffer with the overhead clock and an enable
line.
The AUPC data is stripped from the frame structure and is sent to the M&C via a serial
interface.
10.2.5

Buffer Operation

The buffer has two serial interfaces to the M&C interface. The first serial interface is
used to download the desired buffer size. The second serial interface is used to provide
the M&C with the information necessary to calculate the fill status of the buffer. Three
discrete lines are provided:
•
•
The Doppler buffer receives data clocked by the overhead clock from the Demod and an
enable line from the DEMUX. The data is stored in RAM. Four options are allowed to
clock the data out of the buffer:
•
•
•
•
One line to center the buffer on command.
Two lines to indicate either an overflow or underflow condition.
TX
RX
Internal
External
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MN/SNM1001L.IOM