Arbiter Systems 120A, User Manual

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7 Appendix
7.1 IRIG-B Timecode
IRIG- B is a serial time code developed by the US military’s I nter- R ange I nstrumentation G roup for range. The IRIG-
B timecode has a time frame of 1 second with an index count of 10 milliseconds and contains Time Of Year (TOY)
in days, hours, minutes, seconds, and year information in a BCD format and seconds-of-day in SBS.
Three functional groups of bits in the IRIG-B time code are arranged in the following order: Binary Coded Decimal
(BCD), Control Function (CF) and Straight Binary Seconds (SBS). The BCD group, with IEEE C37.118.1 OFF, contains
only time information including the seconds, minutes, hours and days, recycling yearly. With IEEE C37.118.1 ON,
BCD adds year information. The CF group contains other information including time quality, leap year, pending
leap seconds and parity. Reference bits separate the various components of the IRIG-B time code.
Figure 7-1 illustrates the primary differences between modulated and unmodulated IRIG-B. You will notice that
the while modulated IRIG-B is distinctive because of the 1 kHz sinewave carrier, it is similar to unmodulated IRIG-B
since the peak-to-peak values of the carrier follow the same form as the peaks of the digital waveform, which
contain the information. Note that the first reference bit of both modulated and unmodulated IRIG-B is in sync
with the rising edge of a 1 PPS signal.
Output Signal Description
Figure 7-1: IRIG-B Waveforms
7.1.1 IRIG-B IEEE C37.118.1
As mentioned above, turning IEEE C37.118.1 ON in the clock enables extra bits of the Control Function (CF)
portion of the IRIG-B time code. Within this portion of the time code, bits are designated for additional features,
including:
•
Calendar Year (old method, now called BCD
Y EAR
)
•
Leap seconds, and leap seconds pending
•
Daylight Saving Time (DST), and DST pending
•
Local time offset
•
Continuous Time quality (new with C37.118.1)
•
Parity
•
Position identifiers