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SLM-3650 Satellite Modem
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A.3.4.2
Error Detection
The decoder provides a means to check for uncorrectable RS blocks. The decode Xilinx
monitors the CRTN line out of the RS decoder. CRTN is valid during the first byte of each
RS block. CRTN is programmed such that a low indicates that the last RS block of data
was correctable. If CRTN is high during the first byte, then the last RS block of data
exceeded the correction capability of the RS decoder. If the block is uncorrectable, the data
is passed through the decoder as received, meaning no correction was performed on that
block of data. The decode Xilinx monitors the CRTN line and latches a status line on any
high state. Approximately once every second the M&C reads the status line and reports any
UAS (unavailable seconds) as a stored fault on the modem front panel. The status line is
cleared every time the M&C reads the status. See Figure A-23 for a block diagram of the
RS Decoder.
Figure A-23. Reed-Solomon Decoder Section Block Diagram
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A–76
Revision 3
MN/SLM3650.IOM
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