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.
Element 55 (550 ms) is the ±1.0 millisecond error flag. Element 55 is set to Binary
1 when the expected time error is within +/- 1.0 millisecond, and a Binary 0 dur-
ing all other conditions of operation.
552 SecureSync User Reference Guide
APPENDIX
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