Unformatted text preview: mediate layers within any of the service specifications. CCSDS 201.0-B-3 Page 1-1 June 2000 CCSDS RECOMMENDATION FOR TELECOMMAND: CHANNEL SERVICE 1.3 BIT NUMBERING CONVENTION AND NOMENCLATURE In this document, the following convention is used to identify each bit in an N-bit field. The
first bit in the field to be transmitted (i.e., the most left justified when drawing a figure) is
defined to be “Bit 0”; the following bit is defined to be “Bit 1” and so on up to “Bit N-1”.
When the field is used to express a binary value (such as a counter), the Most Significant Bit
(MSB) shall be the first transmitted bit of the field, i.e., “Bit 0”.
BIT 0 BIT N-1 N-BIT DATA FIELD FIRST BIT TRANSMITTED = MSB In accordance with modern data communications practice, spacecraft data fields are often
grouped into 8-bit “words” which conform to the above convention. Throughout this
Recommendation, the following nomenclature is used to describe this grouping: 8-BIT WORD = “OCTET” By CCSDS convention, all “spare” bits shall be permanently set to value zer...
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