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ISO 11104

3rd Edition, December 15, 2011

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Space data and information transfer systems - Time code formats

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Description / Abstract:

Time codes are digital representations of time information. Four standard CCSDS-Recommended time codes are described (one ‘unsegmented' and three ‘segmented' codes) which use the international standard second as the fundamental unit of time.

An unsegmented time code is a pure binary count of time units and fractional time units from a starting time called the ‘epoch'.

A segmented time code is one in which the count of time units and fractional time units is accumulated in two or more cascaded counters which count modulo of various bases and start from the epoch.

 The four Recommended time code formats carry both the time data (in the TIME SPECIFICATION FIELD, or T-FIELD) and, where applicable, additional information (in the TIME CODE PREAMBLE FIELD or P-FIELD) that uniquely identifies a specific time code format. The P-FIELD may be either explicit or implicit (refer to paragraph 2.1.1).


The purpose of this Recommended Standard is to establish a small number of standardized recommended time code formats for use in data interchange applications between Agencies of the CCSDS. This Recommended Standard does not address timing performance issues such as stability, precision, accuracy, etc.
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