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FAA IRIG B data structure. The BCD time of year provides the day of the year, 001-366, and
the time of day including seconds. The hour of the day is expressed in 24-hour format.
FAA IRIG B General Description
1.
Time frame: 1.0 seconds
2.
Pulse rates:
A.
Element rate: 100 per second
B.
Position identifier rate: 10 per second
C.
Reference marker rate: 1 per second
3.
Element identification: The "on time" reference point for all elements is the pulse leading
edge.
A.
Index marker (Binary 0 or uncoded element): 2 millisecond duration
B.
Code digit (Binary 1): 5 millisecond duration
C.
Position identifier: 8 millisecond duration
D.
Reference marker, 1 per second. The reference marker appears as two con
secutive position identifiers. The second position identifier marks the on-time point
for the succeeding code word.
4.
Resolution: 10 milliseconds
5.
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 FAA
IRIG B code uses five of the Control Function elements to encode satellite lock
status and time error flags. For a description of the status and error flag imple
mentation, refer to the table and the paragraphs below.
Element 53 (530 ms) is the time sync status bit. Element 53 is a Binary 1 when the
receiver locked to GPS, and a Binary 0 when the receiver is not locked to GPS.
422 NetClock User Reference Guide
APPENDIX