Spectracom SecureSync 1200 - Page 550

Figure 5-63: 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 position 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 ele
ments.
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 indicators. 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.
The straight binary (SB) time-of-day code word normally found between position identifiers P
8
and P
0
is eliminated for FAA IRIGB. All elements between position identifiers P
8
and P
0
are set
to Binary0.
534 SecureSync User Reference Guide
APPENDIX