Safran SecureSync 2400 - Page 615

Figure 5-68: FAA modified IRIG B
Notes
The beginning of each 1.0 second time frame is identified by two consecutive
8.0ms elements (P
0
and P
8
). The leading edge of the second 8.0ms element
(P
R
) is the "on time" reference point for the succeeding time code. 10pps pos-
ition identifiers P
0
, P
1
, ..... P
8
(8.0 ms duration) occur 10ms before 10pps "on time"
and refer to the leading edge of the succeeding element.
The time code word and the control functions presented during the time frame
are pulse-width coded. The binary "zero" and index markers have a duration of
2.0ms, and the binary "one" has a duration of 5.0 ms. The leading edge is the
100pps "on time" reference point for all elements.
The binary coded decimal (BCD) time-of-year code word consists of 30 digits
beginning at index count 1. The binary coded subword elements occur between
position identifiers P
0
and P
5
(7 for seconds; 7 for minutes; 6 for hours; 10 for
days) until the code word is complete. An index marker occurs between the
decimal digits in each subword to provide separation for visual resolution. The
least significant digit occurs first. The BCD code recycles yearly.
Twenty-seven control functions occur between position identifiers P
5
and P
8
.
FAA uses this field to communicate satellite lock status and time error and indic-
ators. The first flag element is at 530ms which indicates satellite lock. The ±1ms
error flag occurs at 550ms. The ±5ms error flag occurs at 560 ms. The ±50ms
error flag occurs at 570ms. The ±500ms error flag occurs at 580ms.
SecureSync 2400 User Manual 599
APPENDIX