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 number of seconds elapsed since midnight. The Control Function field con-
tains 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 sep-
aration for visual resolution. 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 SecureSync uses the Control Functions 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 units. Elements
65 through 68 contain the binary equivalent of tens of years. In keeping with IRIG
552 SecureSync 2400 User Manual
APPENDIX
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