The IRIG B code contains the Binary Coded Decimal (BCD) time of year, Control
Function (CF) field and the Straight Binary Seconds time of day. The following fig-
ure illustrates the IRIG B data structure. The BCD time of year provides the day of
the year, 1-366, and the time of day including seconds. The hour of the day is
expressed in 24 hour format. The SBS time is the number of seconds elapsed
since midnight. The Control Function field contains year information and a time
synchronization status bit.
1. Time frame: 1.0 seconds.
2. Code digit weighting:
A. Binary Coded Decimal time-of-year.
Code word - 30 binary digits.
Seconds, minutes hours, and days.
Recycles yearly.
B. Straight Binary Seconds time-of-day.
Code word - 17 binary digits.
Seconds only, recycles daily.
3. Code word structure:
BCD: Word seconds digits begin at index count 1. Binary coded ele-
ments occur between position identifier elements P0 and P5 (7 for
seconds, 7 for minutes, 6 for hours, and 10 for days) until the code
word is complete. An index marker occurs between decimal digits in
each group to provide separation for visual resolution. Least sig-
nificant digit occurs first.
CF: IRIG formats reserve a set of elements known as Control Func-
tions (CF) for the encoding of various control, identification, or other
special purpose functions. IRIG B has 27 Control Functions located
between elements 50 and 78. The VersaSync uses the Control Func-
tions to encode year information and time synchronization status.
The table below lists the Control Function Field and the function of each element.
Element 55 is the time synchronization status bit. Element 55 is a Binary 1
when the unit is in sync, and a Binary 0 when it is not.
Year information consists of the last two digits of the current year (i.e. 97,
98, 99 etc.). Elements 60 through 63 contain the binary equivalent of year
378 VersaSync User Manual
APPENDIX
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