Spectracom NetClock 9400 Series, Руководство пользователя

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Figure 5-11:
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.
424 NetClock User Reference Guide
APPENDIX