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Refer to Figure A-3 for the Reed-Solomon frame format. The term n - k = 2t is the total
number of check bytes appended to the end of the data. The outer Codec reads the data in
blocks of n bytes, and recalculates the check bytes. If the recalculated check bytes do not
match the check bytes received, the Codec makes the necessary corrections to the data
within the data block. The letter n represents the total number of bytes in a given block
of data out of the Codec. The letter k represents the number of data bytes in a given
block. The terms k, n, and t will vary depending on the data rate being used. The Codec
then sends only the corrected data to an output FIFO.
The data is sent through a self-synchronizing 8-bit parallel descrambler in accordance
with the IESS-308 Rev. 6B specification. The descrambler converts the data back into
the original data that the user intended to send. The synchronous descrambler is
synchronized by the detection of the unique word at the end of each Reed-Solomon
frame. The data is then sent to the interface PCB for further processing.
A–6
SDM-9000 Satellite Modem
Rev. 4
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