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 implementation, 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 Bin-
ary 1 when the expected time error is within +/- 1.0 millisecond, and a Binary 0
during all other conditions of operation.
Element 56 (560 ms) is the ±5.0 millisecond error flag. Element 56 is set to
Binary 1 when the expected time error is within +/- 5.0 milliseconds. and a Bin-
ary 0 during all other conditions of operation.
Element 57 (570 ms) is the ±50 millisecond error flag. Element 57 is set to Bin-
ary 1 when the expected time error is within +/- 50 milliseconds, and a Binary
0 during all other conditions of operation.
Element 58 (580 ms) is the ±500 millisecond error flag. Element 58 is set to
Binary 1 when the expected time error is within ±500 milliseconds, and a Bin-
ary 0 during all other conditions of operation.
Table 5-30:
FAA Time Error Indicators
Time Since Loss of Lock Status/Error
Lock Indic-
ator
±1ms ±5ms ±50ms ±500ms
N/A Locked Error < 2μs 1 0 0 0 0
< 00:16:40 Unlocked Error < 1ms 0 1 0 0 0
00:16:41 to 01:23:39 Unlocked Error < 5ms 0 0 1 0 0
01:23:40 to 13:53:19 Unlocked Error < 50 ms 0 0 0 1 0
13:53:20 to 5 days
18:53:19
Unlocked Error < 500
ms
0 0 0 0 1
>5 days 18:53:20 Unlocked Error
Unknown
0 0 0 0 0
N/A Power On 0 0 0 0 0
556 SecureSync 2400 User Manual
APPENDIX
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