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 figure 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 num-
ber 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 elements 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 res-
olution. Least significant digit occurs first.
CF: IRIG formats reserve a set of elements known as Control Functions (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 Ver-
saSync uses the Control Functions to encode year information and time syn-
chronization 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 units. Elements 65 through
68 contain the binary equivalent of tens of years. In keeping with IRIG formats, the least
significant bit occurs first. All unused Control Functions are filled with a space (Binary 0).
278 VersaSync User Manual
APPENDIX
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